Closes #12796

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[ci skip]

Update Ruby version to 2.2.4 (latest previous stable) and update docs

Tests and issues added to https://github.com/gitlabhq/gitlabhq/issues/8696 were all fine after the upgrade. 

Main issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/3340

See merge request !2534

Improve performance of retrieving last update times for events

See 75195eefcca4cb3961986c90c8e837da02f30134 and
https://gitlab.com/gitlab-org/gitlab-ce/issues/12415#note_3387317
for the juicy details.

Related issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/12415

See merge request !2613

Skip the 2FA requirement during logout

See merge request !2581

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Increase contrast between highlighted code comments and inline diff marker.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12737.

It was especially bad in Monokai, better now.

See merge request !2629

Fix CI runner version not being properly updated when asked for a build

Due to broken implementation of attribute_for_keys the runner information was not updated correctly.

This MR adds test to check that such scenario will never happen again.

See merge request !2618

Return a 404 instead of a 500 when accessing a non-existent group

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/3352

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/5600

See merge request !2614

Limit jquery-ui requires to what we actually use



See merge request !2274

Update wording for 2FA requirement notice



See merge request !2582

Remove link from system hook

Closes #12672

See merge request !2588

Bump octokit to `~> 3.8.0`

Closes #2877

See merge request !2536

Fix hot reloading for CI API



See merge request !2617

Due to broken implementation of attribute_for_keys the runner information was not updated correctly.

This MR adds test to check that such scenario will never happen again.

Refactor forking workflow documentation

Closes #5974 

See merge request !2623

[ci skip]

By simply loading the first event from the already sorted set we save
ourselves extra (slow) queries just to get the latest update timestamp.
This removes the need for Event.latest_update_time and significantly
reduces the time needed to build an Atom feed.

Fixes gitlab-org/gitlab-ce#12415

Use generic method to checks if artifacts are available

Closes #12626

See merge request !2576

Fix typo on artifacts doc



See merge request !2622

[ci skip]

[ci skip]

Update ExternalIssue regex for JIRA integration

The pattern in the `::reference_pattern` class method in the
`ExternalIssue` model does not match all valid forms of JIRA project
names. I have updated the regex to match JIRA project names with numbers
and underscores. More information on valid JIRA project names can be
found here:
https://confluence.atlassian.com/jira/changing-the-project-key-format-192534.html

* The first character must be a letter,
* All letters used in the project key must be from the Modern Roman Alphabet and upper case, and
* Only letters, numbers or the underscore character can be used.

See merge request !2598

The pattern in the `::reference_pattern` class method in the
ExternalIssue model does not match all valid forms of JIRA project
names. I have updated the regex to match JIRA project names with numbers
and underscores. More information on valid JIRA project names can be
found here:
https://confluence.atlassian.com/jira/changing-the-project-key-format-192534.html

* The first character must be a letter,
* All letters used in the project key must be from the Modern Roman Alphabet and upper case, and
* Only letters, numbers or the underscore character can be used.

Bug/jschatz1/file browser lines

Fixes #12725 

![Screen_Shot_2016-01-26_at_11.19.39_AM](/uploads/c5f5a143926600e02de4cfc0687ed8dd/Screen_Shot_2016-01-26_at_11.19.39_AM.png)


See merge request !2615

Bump Workhorse version to 0.6.2

Fix for #12634 has been introduced in gitlab-org/gitlab-workhorse!34.

See merge request !2616

Merge branch 'search-box-in-group-members-view-is-too-small-for-placeholder-in-chrome' into 'master'

Fixes: Search box in Group Members view is too small for placeholder in Chrome

Fixes #2498 

![Screen_Shot_2016-01-25_at_11.55.57_PM](/uploads/de4fda98cd8552641208b3a7a9277e35/Screen_Shot_2016-01-25_at_11.55.57_PM.png)


See merge request !2609