Use tag_exists? in GitAccess#protected_tag?

This will fail until https://gitlab.com/gitlab-org/gitlab_git/merge_requests/81/ is merged. Adding this should speed up checking for tags in `Gitlab::GitAccess` as it no longer needs to retrieve the entire list of tags.

See https://gitlab.com/gitlab-org/gitlab-ce/issues/14280 for more information.

See merge request !3983

Previously this method would directly receive the output of tag_name().
This method could either return a String or nil. In the previous setup
this would somehow magically work but because Rugged::TagCollection#[]
doesn't accept nil values it started to fail.

To work around this the elsif in change_access_check() assigns the
result of tag_name() to a local and then _only_ calls protected_tag?()
if the tag name is not nil. The extra parenthesis are put in place to
ensure that things are parsed correctly, without these the code would be
parsed as follows:

    elsif tag_ref = (tag_name(ref) && protected_tag(tag_ref))

During runtime this would basically resolve to:

    elsif tag_ref = (tag_name(ref) && protected_tag(nil))

This is because when you refer to the variable you're assigning _in_ the
assignment Ruby returns nil instead of raising an error.

This removes the need for retrieving the entire list of tags just to
check if a specific one exists.

Moved entry for !3880 to 8.7.2

See merge request !4058

Apparently this was already released in 8.7.2 but no changelog entry was
added.

[ci skip]

Added CHANGELOG entries for !3880 and !3931

See merge request !4057

[ci skip]

[ci skip]

Upgrade Sidekiq to 4.1.2

Fixes a memory leak: https://github.com/mperham/sidekiq/commit/a2bdb875fe495bc28b1bee80120e4a5641ca0731

See merge request !4056

Fix the line code when importing PR review comments from GitHub

Pull Request Review Comments are comments on a portion of the unified diff.

Closes #17205

See merge request !4010

Pull Request Review Comments are comments on a portion of the unified
diff.

15179 builds page redesign

Closes #15179   

<img src="/uploads/d9ec515e500dc9023d588b5c38636a86/Screen_Shot_2016-04-26_at_1.35.11_PM.png" width="800px">

Updated screenshot:   
<img src="/uploads/63109057ee271d788ab726e52acf9328/Screen_Shot_2016-05-04_at_9.23.01_AM.png" width="800px">

Updated screenshot with count badges instead of parentheses:  
<img src="/uploads/d9cd91b079d23c63601c8dbcf4803c8d/Screen_Shot_2016-05-05_at_7.40.48_AM.png" width="800px">

See merge request !3935

Moved TeamCity changelog entry to 8.7.3

See merge request !4049

[ci skip]

Log to application.log when an admin starts and stops impersonating a user

Closes gitlab-org/gitlab-ee#536

See merge request !4028

Use new build badge URLs

Use new build badge URLs to follow the instruction at [the project badges](https://gitlab.com/gitlab-org/gitlab-ce/badges).

See merge request !4037

Merge request widget displays TeamCity build state and code coverage correctly again

## What does this MR do?
This MR contains a fix for a regression introduced in `8.7`. In former version, the TeamCity build status was always displayed correctly. In `8.7` the build state is still checked, but the UI is not updated correctly any longer.

## Are there points in the code the reviewer needs to double check?
The changes are quite simple, so please simply double check them.

## Why was this MR needed?
This MR is needed to make the TeamCity build status working again.

## What are the relevant issue numbers?
#17080 

See merge request !3998

Use `number_to_human_size` helper to show repository size

This will intelligently format large repository sizes in GBs (or,
shudder, TBs).

Also, removes `rescue` clause from `repository_size` helper.
The repository size has since become calculated (and cached)
more intelligently, and this should no longer be necessary.

See merge request !4047

The repository size has since become calculated (and cached) more
intelligently, and this should no longer be necessary.

This will intelligently format large repository sizes in GBs (or,
shudder, TBs).

Sanitize repo paths in new project error message

Closes #17243

See merge request !4029

Closes #17243

Remove break-all from links

Closes #17000

See merge request !4042

Fix file list page border colors



See merge request !4008

Improve milestone page UI

* remove button after edit button
* use hex value for text color
* re-use existing text color variables
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !4014

Expire repository exists? and has_visible_content? caches after a push if necessary

See merge request !3975

Closes #17012

Remove unused .contributed-projects class

While working on #13401 and trying to add a new tab to the user profile
page, I came across this. I noticed that the `contributed-projects`
class was only being used in order to select the div in the tests. For
consistency with the other tabs, I decided to remove this class and use
the div's id for the selector.

See merge request !3945

Limit the number of merge requests per project to avoid long seeds in development environment

This step was taking a long time because seed_fu creates N / 2 merge requests for each repo, where N is the number of branches for that repo. At the time of this writing, there are 234 branches on the gitlab-ce repo, leading to 117 merge requests.

See merge request !4032