Added specs for Issue#referenced_merge_requests

Added these while looking into https://gitlab.com/gitlab-org/gitlab-ce/issues/13651.

See merge request !3125

Add shortcut to toggle markdown preview

Allow to toggle markdown preview with shortcut `ctrl+shift+p` (`cmd+shift+p` on OSX).

- If the user is focused on a md textarea, `ctrl-shift-p` will show the preview, otherwise native browser event is fired
- The textarea is re-focused after disabling the preview tab
- Results of markdown render is cached for fast toggles

I'm on linux, so if someone can test it on OS X, it would be great!

Closes #14038

See merge request !3111

Retry bundler and apt-get



See merge request !3146

Fixed the GitPushService specs

See merge request !3139

Add a `gemojione:sprite` Rake task

This task will generate a standard and Retina sprite of all of the
current Gemojione Emojis, with the accompanying SCSS map.

It will not appear in `rake -T` output, and the dependent gems are not
included in the Gemfile by default, because this task will only be
needed occasionally.

See merge request !3130

Fix error 500 in Todos

Closes #14095 

Closes #14075 

Closes #14109

Closes #14151

See merge request !3141

This task will generate a standard and Retina sprite of all of the
current Gemojione Emojis, with the accompanying SCSS map.

It will not appear in `rake -T` output, and the dependent gems are not
included in the Gemfile by default, because this task will only be
needed occasionally.

[ci skip]

Snippet visibility badge spacing

Closes #14074 

![Screen_Shot_2016-03-08_at_08.40.32](/uploads/f55ca724fbf0e247b299a2702c3b55f5/Screen_Shot_2016-03-08_at_08.40.32.png)

See merge request !3122

Commit limits

Prevent timeouts when creating/viewing Merge Requests with many
commits. Also, reduce the number of commits shown in the UI from 500
to 100.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/14031

This MR avoids Unicorn timeouts in some places and takes 4.5 seconds
off load times in others, when manually testing with a 4500-commit
compare/MR in the linux repo. It does not limit the number of Commit
objects instantiated in memory, just the amount of HTML generated. It
seems that having 4500 commits objects is not a problem in itself. If
it ever becomes one we could do something for Commit objects like we
did for Diff (introduce a CommitCollection or something).

See merge request !3095

Bump poltergeist to `~> 1.9.0`



See merge request !3116

This fixes the remainder of the GitPushService specs.

These were broken by commit 21a05328.
Two JIRA tests remain broken but I can't quite figure out how to fix
them.

Retry failed tests

This is to make the CI builds more reliable due to large amount of timeouts and deadlocks recently.


See merge request !1793

Fix bug where Bitbucket 'closed' issues were imported as 'opened'

_Originally opened at !2930 by @iurisilvio._

- - -

Bitbucket has an undocumented status `closed`.

https://confluence.atlassian.com/bitbucket/issues-resource-296095191.html

Related to https://gitlab.com/gitlab-com/support-forum/issues/559

See merge request !2973

See merge request !3136

This wasn't included in gitlab-org/gitlab-ce!3000.

Fix master branch link to upgrader.md



See merge request !2967

Make better use of the `visibility_level` factory traits



See merge request !3131

Remove `Snippet#expires_at`

This was removed from the interface in
https://github.com/gitlabhq/gitlabhq/pull/6027 but its implementation
lingered around for two years.

See merge request !3103