Improve performance of sorting milestone issues

This will fix the problem described in #3066.

See merge request !1609

This cuts down the time it takes to sort issues of a milestone by about
10x. In the previous setup the code would run a SQL query for every
issue that had to be sorted. The new setup instead runs a single SQL
query to update all the given issues at once.

The attached benchmark used to run at around 60 iterations per second,
using the new setup this hovers around 600 iterations per second. Timing
wise a request to update a milestone with 40-something issues would take
about 760 ms, in the new setup this only takes about 130 ms.

Fixes #3066

Add ability to remove the fork relationship from project settings

![Screen_Shot_2015-10-18_at_12.37.24](/uploads/676571642a4c90f7f286280d714599a3/Screen_Shot_2015-10-18_at_12.37.24.png)
![Screen_Shot_2015-10-18_at_12.37.28](/uploads/1a069ecfc4cd3b5438772a9c3f04b6fc/Screen_Shot_2015-10-18_at_12.37.28.png)

Replaces !1579.

Fixes #2578.

See merge request !1636

Close issues mentioned in MR description when MR is merged using
fast-forward merge or when merge commit message is edited.

Fixes gitlab-org/gitlab-ee#48.

See merge request !1639

Allow users to select the Files view as default project view


![Screen_Shot_2015-10-17_at_19.24.01](/uploads/c3194db856f5e5e1b3493302c0a479a5/Screen_Shot_2015-10-17_at_19.24.01.png)

Also shows the readme at the very bottom, like on the regular Files page.


Replaces !1489.

Closes #2655.

See merge request !1632

[ci skip]

Fix bug where a push would only create cross references from the first commit.

Apparently we can't `return` from a `Hash.new` block. Who knew.

See merge request !1638

Fix spelling of Description

Show merge requests which close current issue

Closes #2903

### What does this MR do
If an issue is to be closed by a merge request the current user has access to, this will be displayed when the user looks at the issue.

![Screenshot_from_2015-10-12_12-10-37](https://gitlab.com/zj/gitlab-ce/uploads/52e429704e73067b24b69801f13ad7bc/Screenshot_from_2015-10-12_12-10-37.png)

/cc @DouweM

See merge request !1569

Fix padding of outdated discussion item.

Old:

![Screen_Shot_2015-10-16_at_09.29.17](https://gitlab.com/gitlab-org/gitlab-ce/uploads/d715debebe54d27c2eed7c22843e886c/Screen_Shot_2015-10-16_at_09.29.17.png)

New:

![Screen_Shot_2015-10-16_at_09.29.23](https://gitlab.com/gitlab-org/gitlab-ce/uploads/7c0c033adade92cb16406c027cb4c010/Screen_Shot_2015-10-16_at_09.29.23.png)

It still looks the same when the discussion is expanded.

See merge request !1614

Fix nonatomic database update potentially causing project star counts to go negative

The `counter_cache` decrement function is called when a project star is deleted,
but there was no guarantee multiple workers would not attempt to delete the
same item simultaneously. Use an atomic update to prevent the count from going negative.

Note: I was only able to duplicate the issue on GitLab.com, but I haven't been able to replicate it anywhere else. Presumably this bug happens when the `WHERE` clause takes some time to search for the right entry and multiple requests get sent simultaneously. Need to verify whether this fix truly solves the issue.

Closes #3067

See merge request !1628

Separate rendering of Markdown reference links from redacting those the user doesn't have access to and extracting referenced objects

Related: !1014

See merge request !1090

Temporary bring /ci page page with help information
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1630

Redirect old CI project route to GitLab project
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1629

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

Hide Builds tab is GitLab CI is not enabled
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1627

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

The counter_cache decrement function is called when a project star is deleted,
but there was no guarantee multiple workers would not attempt to delete the
same item simultaneously. Use an atomic update to prevent the count from going negative.

Closes #3067

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

Allow dashboard and group issues/MRs to be filtered by label

See merge request !1591

Fix import from SVN link

See merge request !1617