Fix resolving conflicts on forks

## What does this MR do?

When we resolve conflicts, we create a merge commit in the source branch with parents `[source_branch_head, target_branch_head]`. But when the MR is from a fork, `target_branch_head` might not exist in the source repo at all, so we need to fetch it if it isn't there. We can do this locally so it should be fast.

## Are there points in the code the reviewer needs to double check?

The `TestEnv` changes are needed to reset the branch refs if we're reusing a git directory locally - otherwise, there might not be conflicts!

## Why was this MR needed?

It's a bug in a new feature!

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Closes #21459.

See merge request !6082

Fix diff comments on legacy MRs

Allow diff commenting on MRs without complete diff refs. (Commenting would work before, but the JSON response would fail, so you'd only see your comment after a refresh.)

Is this really all I needed to do? I feel like there must be more to it 😊

It's a regression!

Closes #21211.

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !6029
Conflicts:
	spec/features/merge_requests/diff_notes_spec.rb

docs: make sure to update 8.10-to-8.11 workhorse version too (see !5983)

## What does this MR do?

Make sure to remember the correct workhorse version for specific version update instructions for those of us still doing source installs.
Related to !5983.

See merge request !6049

Check for pipelines when setting page_gutter_class.

## What does this MR do?

Fixes regression issue related to the MR window sliding behind the right sidebar on page refresh. 

## Are there points in the code the reviewer needs to double check?

I'm getting stuck thinking about if/how to test this. Or maybe it just deserves a note somewhere about remembering to update `page_gutter_class` when a new route is added?

## Why was this MR needed?

This regression prevented users from using many features of the MR view.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/21121

## Screenshots (if relevant)

Before: 
![Screen_Shot_2016-08-23_at_11.08.04_AM](/uploads/bad1a83569022a7fc699a978c5abef62/Screen_Shot_2016-08-23_at_11.08.04_AM.png)

After: 
![Screen_Shot_2016-08-23_at_11.07.46_AM](/uploads/6cbcb2f849c68dfc93d8a4b53089b06e/Screen_Shot_2016-08-23_at_11.07.46_AM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [ ] Added for this feature/bug
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

cc: @jschatz1 

See merge request !5952

Fix enormous IE11 fork button

## What does this MR do?
Puts a width on btn SVGs because IE can't handle `auto`

## What are the relevant issue numbers?
Closes #21099

See merge request !5982

Use new image for Issue Board page

Replace the Issue Board image with a new one

See merge request !6013

Fix wrong Koding link



See merge request !6030

Automatically expand hidden discussions when accessed via a permalink hash (closes #19304)

## What does this MR do?

Addresses "Auto-expand a discussion note when we arrive via anchor" (issue #19304)

## Are there points in the code the reviewer needs to double check?

Let me know if the code is consistent with community standards (not 100% sure about indentation of chained jQuery actions)

I don't think this MR warrants any unit tests or documentation, but let me know if you disagree.  I'll add the requisite CHANGELOG entry upon approval.

## Why was this MR needed?

Currently, if a discussion is accessed via a permalink to an "outdated" diff discussion, the anchor will not bring you to the expected part of the page.

## What are the relevant issue numbers?

#19304 

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)


See merge request !5585

Label list shows all issues (opened or closed) with that label

## What does this MR do?

Change the label list to shows all issues (opened or closed) with that label.

## What are the relevant issue numbers?

Closes #21257

See merge request !5991

Handle non-UTF-8 conflicts gracefully

## What does this MR do?

If a conflict file isn't in a UTF-8-compatible encoding, we can't resolve it in the UI.

## What are the relevant issue numbers?

Closes #21247. 

See merge request !5961

Fix changelog



See merge request !6035

Fix external issue tracker "Issues" link leading to 404s

## What does this MR do?

This MR fixes the redirection to the wrong URL when using an external issue tracker, such as JIRA or Redmine.  a70431f8 modified the behavior to link to the external issue tracker
issues URL instead of the project path URL. This restores the previous behavior.

## Why was this MR needed?

The issues URL often has `:id` associated with it for linking mentioned issues.
For external issue trackers, the project page is the intended target.

## What are the relevant issue numbers?

Closes #21252

Related to #21402

See merge request !6006

Handle unavailable system info

## What does this MR do?

Handle the case where we can't get system info without blowing up. As this is the first tab in the monitoring section, it's difficult to get to the other tabs if this page throws a 500. Also be more specific about the info we want, so we don't fail on something we don't care about (like `/proc/net/dev`).

## Why was this MR needed?

grsecurity can prevent users from reading `/proc`, which is what Vmstat uses to find CPU and memory info.

## What are the relevant issue numbers?

Closes #21378.

See merge request !5989

last_push_event widget considers fork events on the main project

Push events on the fork of the current project are considered to be shown besides the push events on the current project. Before we just consider fork events if exists a fork so we miss current project events if the current user has a fork.

Closes #20254

See merge request !5978

Does not halt the GitHub import process when an error occurs

## What are the relevant issue numbers?

Fixes #20385 

https://gitlab.com/gitlab-org/gitlab-ce/issues/20149

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5763

Use gitlab-workhorse 0.7.11

Versions 0.7.9 and 0.7.10 crash on previously valid 'authBackend'
settings.

I don't know how many people are affected by this, 'normal' Omnibus
installations are not. (If they were gitlab.com would have stopped
working :) ). Still this is something we should not ship.
Unfortunately 8-11-stable uses 0.7.10 (but 8.11.0 does not). So I
think we need to put this in the next 8.11 patch release.

See merge request !5983

Change slash commands docs location



See merge request !5937

Document protected branches new behavior



See merge request !5934

Documentation for Issue Boards

## What does this MR do?

Add documentation for issue boards.

## What are the relevant issue numbers?

- Issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/17907
- Backend MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5548
- Frontend MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5554

See merge request !5713

Split Koding admin/user docs

Backend/Frontend MR https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5909

See merge request !5938

Add Ruby 2.3 upgrade notes.

The 8.10 to 8.11 docs didn't mention Ruby 2.3, now they do.

See merge request !5940

Fix location of markdown help

Resolves #21208, and incorrect link to the markdown style guide

See merge request !5945

Fix for update 8.10-to-8.11.md doc.

Fixed a typo in the docs to update Ruby.

See merge request !5941

Remove tab stop from issuable form added by description templates

See merge request !5929

Fix typo in gitlab-workhorse header

See merge request !5891

Bump SimpleCov merge timeout to 365 days

## What does this MR do?

In case that CI pipeline fails because of intermittent errors in one of the jobs, when someone retries the only failing job located in the middle stage, the job that calculates compound coverage that is configured in later stage, and triggered after retrying job in the pipeline, will still return an accurate coverage value.

Closes #21144

See merge request !5932

Fixed enter key in search input not working

## What does this MR do?

Fixes a bug where the enter key wouldn't search in the top nav search input

Closes #20627 

See merge request !5888

Fix project namespace links

#### What does this MR do?
Fixes pipeline links

#### Why was this MR needed?
Links went to a 404 on fork MR pipelines tab

#### What are the relevant issue numbers?
Closes #21107

See merge request !5912

Fix incorrect "stopped impersonation" log message

Minor bug: Usernames were swapped in the log message.

Closes #21015

See merge request !5949

Also check if Akismet is enabled, before showing the `Submit as spam` button.

Fixes #21229

See merge request !5948

Fix Spinach branches spec

I broke master by adding a branch to gitlab-test for https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5961, which put the branch in this scenario off the first page 😆 

See merge request !5964

Fix file links on project page Files view

## What does this MR do?

Fix the project show page when the default view is set to Files so that the links work.

## Are there points in the code the reviewer needs to double check?

I can't figure out what caused this to break 😕 

## What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-com/support-forum/issues/959.

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md) (N/A)
- [x] API support added (N/A)
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5933