Conditionally remove indices that may not exist in pre-GitLab v6.7 installations

In pre-GitLab v6.7 installations, the `tagging` indices were directly added to the init schema and not added in a migration. Anyone using this older DB schema may not have these indicies, so only remove them if they are there.

Closes #1593

See merge request !626

Closes #1593

new issue after release

See merge request !1810

Fix tooltips for event filter links

See merge request !618

Improve handling of large diffs

Diffs with a large number of changed lines time out (504 HTTP error) or
generate a HTML page that's so heavy web browsers struggle with it.

https://github.com/gitlabhq/gitlabhq/pull/5014 introduced limits on
commit line count so that only a safe portion is rendered. This was
later undone by code refactoring in be5b6db8, e0eb4803 and c741fcab.
This patch re-introduces a safe limit on number of lines.

See merge request !539

Fix bootlint issues on git clone holder bar

Add yanking pkg example to the release documentation.

See merge request !1809

Make the first branch pushed to an empty repository the default HEAD

In an empty repository, pushing a new branch not called "master" would leave HEAD in an unknown state, causing ambiguity if another branch were pushed. This could in turn cause a new protected branch to be created and cause the default branch to change.

* Closes #1561
* Closes #1576
* Closes https://github.com/gitlabhq/gitlabhq/issues/8883

See merge request !614

revert bad link in documentation

See merge request !1808

Added link reset root password

Added text to link "How to reset root password"

cc/ @sytse

See merge request !1799

Add Markdown feature specs for markup inside links

It was already working, just want to make sure we don't break it in the future.

See merge request !619

It was already working, just want to make sure we don't break it in the
future.

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Refactor mr form

* re-use issuable form for new mr page
* small UI improvements to MR compare and new pages

See merge request !616

Small UI improvements to make project sidebar more neat

* make sidebar blocks more compact
* make clone panel smaller for better aspect ratio
* make `forked from` section cleaner

Screenshot:

![Screenshot_2015-05-06_16.42.12](https://gitlab.com/gitlab-org/gitlab-ce/uploads/69723db619ae7ae4d9551f6340d45384/Screenshot_2015-05-06_16.42.12.png)

cc @rspeicher

See merge request !617

Single docker image

See merge request !1805