Changed sudo by su -c

The sudo command needs a tty to run. If you put this file on a CentOS 6, for example, it will not run in the host startup process. Instead, the 'su -c' runs the command apart if it has or not a tty.

I tested this change in a fresh install of gitlab on a CentOS 6.5 with successful.
Update merge_request_observer_spec.rb
Fix another instance of "created at"

Replace it with "created on".

Change-Id: Ibd26bf82d2e64f142a4f3be6da7701e5b035602f
Don't send an email for "mentioned in" notes

Currently, an email is sent every time a mentionable is referenced
by an issue, a commit or a merge request: if I comment "This MR is
related to #5", watchers get one email for the comment, and another
one stating "Issue #5 was mentioned by issue #13".

This is annoying — but the biggest issue is when pushing an existing
branch. Every issue referenced by commit messages in this branch will
get a new mention (which is fine), and dozens of emails will be sent
for all these new mentions (which is not).

This commit fixes the spam by avoiding to send an email when a new
mention is created. In most cases the email notification for the
mentioner is enough.
Update user_management.md

Believe the intention was to say 'groups' instead of 'projects' here.
Fix registration error info typo
Add .adoc file extension for AsciiDoc

Add .adoc file extension for AsciiDoc as it's a very popular extension to use and the one recommended by the Asciidoctor project.
Database doc changes to address #2412 and #6451.
Fixed Unicorn-Sidekiq confusion in GitLab init script.

There were a few places in the included init script where
Unicorn was referred to as Sidekiq and vice-versa.

This fixes #126.
Switched line endings to LF for system_hooks.md

It was checked in with Windows style line endings.
Do not allow password reset for ldap user.
Deploy key needed documentation.
Split up the lines for Jacob.
 Merge branch 'ldap_password' into 'master'

Prevent LDAP users from using reset password function
Added Slack service integration.
Fix travis setup
Merge pull request #6550 from razielgn/slack-integration

Added Slack service integration.
Merge branch 'master' of github.com:gitlabhq/gitlabhq
Merge pull request #6558 from tsigo/master

Fix travis setup
Speed up features/notes_on_merge_requests_spec

This spec featured the slowest tests in the entire suite. After some
debugging, the cause was found to be the large commit diff generated by
comparing the stable and master branches.

To fix this, the seed repository was modified to create a simple branch
off of master that consists of three simple commits and minor changes.
The spec was then updated to compare master to this branch instead of
stable. The result is a spec group that runs in under 30 seconds, down
from about 90.