Select files with diff filter for graph log

Fix the `service gitlab restart` command

Postgress db migrate fails.(5.4=>6.0)

This commit addresses two related issues:
- Sidekiq should shut down completely before we restart it;
- If we restart unicorn with USR2 we need to kill the old master and
  worker processes.

Added assets:precompile in upgrade guide 5.4 -> 6.0

Fix bug in ace-src-noconflict with Relative url.

Render not found when failing to look for commit

1. Replace params key 'q' with 'extended_sha1'. A extended SHA1 syntax is explained in 'man gitrevisions'.
2. Change the placeholder of looking for commit.
3. Change the label of ref filter.

fix checkout tag name

If we doesn't use a relative url we have this:
<pre>gon.relative_url_root=""</pre>
Else <pre>gon.relative_url_root="/gitlab"</pre>

Gitlab::Application.config.assets.prefix contains:
<pre>/assets</pre>

Update to gitlab-shell 1.7.0 during 5.4-6.0 update