If kerberos is enabled require it

Since 'group: :kerberos' got [included in the Gemfile ](https://gitlab.com/gitlab-org/gitlab-ce/commit/2391a43a7073b4e723e9ca1f7ff19b30f8e51452) Kerberos no longer got [loaded when the app started](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/config/application.rb#L6)

This caused `Devise::OmniAuth::StrategyNotFound` error once Kerberos is enabled, failing to start GitLab .

With this we hopefully do not need to remove group from the Gemfile.

See merge request !819

Fixes for RC2

we need it to make GitLab works with new CI

cc @jacobvosmaer

See merge request !1864

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

Look for .gitlab-ci.yml only if checkout_sha is present

Fixes https://dev.gitlab.org/gitlab/gitlabhq/issues/2396

cc @vsizov

See merge request !818

Update install docs for 7.12

See merge request !1857

Even though the 7-12-stable branch does not exist yet.

Git 2.1.2 does not protect against pushes trying the '.Git/config'
attack (CVE-2014-9390). Going to 2.4.3 is perhaps a big jump but why not
use the latest? (Famous last words.)

Remove text since rss is now to prominent.

See merge request !1855

Fix link to howto_rc1.md

The relative link that was there before breaks when you copy-paste the
issue template into an actual issue.

See merge request !1856

The relative link that was there before breaks when you copy-paste the
issue template into an actual issue.

Prepare feature steps for RSpec 3

See merge request !803

There's a naming conflict between Capybara and rspec-matchers which both
define the `all` method.

See https://github.com/jnicklas/capybara/issues/1396

Add a note that changing example configuration files requires changing omnibus-gitlab.

Keeping track of changes in these files is not easy and they usually require change in omnibus-gitlab.

Added a note so everyone is aware of this.

Similar is added to gitlab-shell and gitlab-ci.

Discussed in gitlab-org/omnibus-gitlab#605

See merge request !800

Refactor accept merge request widget

* make each case a simple view
* separate  merge request JS from merge request accept widget JS
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !799

Fix graph width on different screen sizes
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !802

Make commit calendar size depend on window size
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !801

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

Add negative tabindex to Markdown Write and Preview tabs

Closes #1757

See merge request !796

An `in_namespace` scope is already present

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

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

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

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

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

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

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

[Docker][Documentation] Uses correct docker image from Docker Hub

[Docker][Documentation] Uses new docker data image from Docker Hub (*sytse/gitlab-data*). Uniform tag name for data image is now *gitlab-data*.

Info about namespaces

Added info about namespaces in groups.

Because of tweet https://twitter.com/kaystrobach/status/603912904757420032

See merge request !1835

Update grids for 2FA details

Also adds a link to the documentation.

Closes #1758

See merge request !795