Added note: working copy changes should be stashed before update process

Originally proposed by @aral in !1043.

Added note: working copy changes (e.g., deleted vendor folder) should be stashed before beginning the update process.
We should probably include this notice on all update guides.

See merge request !2668

Support Akismet spam checking for creation of issues via API

Currently any spam detected by Akismet for non-members via API will
be logged in a separate table in the admin page.

Closes #5612

See merge request !2266

Improve tooltips on admin menu

See merge request !2673

Added dropdown to list all projects on project header

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/4212

When clicking the current project name, it shows a dropdown menu with a list of all projects for that group or user.

When closed:

![Screen_Shot_2016-01-14_at_19.17.44](/uploads/a7258ba388dba238fc2f0468711fc729/Screen_Shot_2016-01-14_at_19.17.44.png)

When open:

![Screen_Shot_2016-01-14_at_19.17.51](/uploads/716533d9eb44b123c5fdff36a4740489/Screen_Shot_2016-01-14_at_19.17.51.png)


cc. @jschatz1

See merge request !2438

[ci skip]

Consistent rails_socket use.

[ci skip]

See merge request !2596

Send raw Git blobs via gitlab-workhorse



See merge request !2451

explicitly call script with bash for consistency

simpler than telling users to set script executable

[ci skip]

See merge request !2621

Bump New Relic gem version to avoid warnings in Web page

This version has support for Grape, so we should consider removing
the newrelic-grape gem as well:

https://docs.newrelic.com/docs/agents/ruby-agent/frameworks/grape-instrumentation

See merge request !2578

Fix add_pagination_headers to keep request parameters in Link header

Originally opened at !2321. Closes #5904. /cc @Michi302

See merge request !2674

Updated contributing guide for stable releases

[ci skip]

See merge request !2638

Lazy Git blobs

To prevent madness like loading a 100MB file into Ruby's memory just
to decide whether it is binary or text.

See merge request !2663

Currently any spam detected by Akismet by non-members via API will be logged
in a separate table in the admin page.

Closes #5612

Allow "@" in file names and path

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/4111

See merge request !2665

Generate valid (RFC 2111) Message-ID in email rejection mailer

Use a Message-ID that is RFC 2111 compliant. This fix is consistent with
how the Message-ID is generated in the 'notify' mailer.

See merge request !2656

Fix typo indentation in CI projects' API



See merge request !2561

Add notes about the regression issues to CONTRIBUTING.md

[ci skip]

See merge request !2661

Expand Git instrumentation

This instruments some extra `Gitlab::Git` code as well as a collection of `Rugged` constants.

See merge request !2664

Fixes #12784