Add a system note and update relevant merge requests when a branch is deleted or re-added

If a branch is deleted with an open merge request, amended offline, and then pushed again,
GitLab doesn't bother to update the merge request even though the last commit ID and/or
code may have changed. This MR ensures that each push will update any relevant merge
requests and adds a system note if this happens as well.

The new messages look like:

![image](https://gitlab.com/gitlab-org/gitlab-ce/uploads/6581eea069cd8e485b7fa4187ed4c043/image.png)

Closes #2926 

See merge request !1601

Implement when syntax in .gitlab-ci.yml

See merge request !1606

[ci skip]

Also adds a preamble note that a working 8.0 installation (i.e.,
gitlab-git-http-server, updated Nginx/Apache configs) is required before
proceeding.

[ci skip]

[ci skip]

Sentences end in periods.

[ci skip]

See merge request !1604

Prepare 8.1 documentation

[ci skip]

See merge request !1612

Update redcarpet gem. Fixes gem memory leak

Fixes #2773 

See merge request !1607

Build View UI fixes



See merge request !1608

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

Markdown typography CSS fixes

The `!important` flags recently added to the `md-typography`
mixin's `pre` elements were overriding the background and
foreground colors for syntax highlighting.

| Before | After |
|:------:|:-----:|
| ![Screen_Shot_2015-09-25_at_3.32.32_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/802163bd9f46864ac89e7be165951f07/Screen_Shot_2015-09-25_at_3.32.32_PM.png) | ![Screen_Shot_2015-09-25_at_3.33.30_PM](https://gitlab.com/gitlab-org/gitlab-ce/uploads/6be72036653378405320085324dff5ad/Screen_Shot_2015-09-25_at_3.33.30_PM.png) |

See merge request !1442

Improve invalidation of stored service password if the endpoint URL is changed (V2)

New version of !1583, using the same failproof logic but this time mirroring the name and behaviour of the change-tracking methods of ActiveModel::Dirty in order to make it clearer and more natural.

Added more tests to clarify the expected behaviour.

This is an alternative to !1594

/cc @vsizov @rspeicher

See merge request !1600

Improve User.by_login performance

This greatly speeds up the performance of `User.by_login`. I adopted some changes from @haynes in this patch, the credits go to him for coming up with those originally.

Fixes #2341

See merge request !1545

Let gitlab-git-http-server handle archive downloads

This change relies on changes in gitlab_git and gitlab-git-http-server.

fixes #2429

See merge request !1548

Added builds view

![Screen_Shot_2015-10-13_at_19.02.48](https://gitlab.com/gitlab-org/gitlab-ce/uploads/95bb3a7d9d603678fdd077558637045d/Screen_Shot_2015-10-13_at_19.02.48.png)

/cc @dzaporozhets @vsizov 


See merge request !1593

Fix error preventing displaying of commit data for a directory with a leading dot

Directories with leading dots erroneously get rejected by the route controller if git
ref regex is used in constraints. This prevents commit data from being loaded. The regex verification is now done in controller.

Closes https://github.com/gitlabhq/gitlabhq/issues/8763


See merge request !1574

Remove guard-rspec and its supporting gems



See merge request !1551

Password can now be specified at the same time as the new URL, and the service
template admin pages now work.

In these particular instances we can just use HAML tags directly. This
can shave off some time spent loading issue pages, though this depends
on the amount of comments being displayed.

When viewing https://gitlab.com/gitlab-org/gitlab-ce/issues/2164 locally
these changes reduce loading time by about 400 ms in total.

By comparing objects in Ruby we can greatly improve the performance of
this method. In the worst case (should no data be eager loaded) this
will run the same amount of queries as before, in the best case (when
data _is_ eager loadeD) it requires no queries at all.

The added benchmark used to produce around 273 iterations per second.
With this commit this has been increased to almost 40 000 iterations per
second: a speedup of roughly 145 times.

Combined with eager loading Note associations this results in about 30
queries less when viewing a single issue, this in turn cuts down the
loading time by 30-40%.

This ensures that when viewing an issue each note already has the
associated project, project members, group and group members available.
Since this information is requres for every note this results in quite
the reduction of SQL queries being executed.