Allow filtering issues that have no milestone or assignee

Correct usage of "Can't"

Fix current class for hooks tab in admin section

Signed-off-by: Martin Bastien <martin.bastien@studiofrenetic.com>

GFM Refactoring

Makes use of 'extended' patterns to add comments to the groups, and also
reduces the total number of groups to just those that are used.

Continues #1222

Closes #1222

Fix invalid syntax in OmniAuth initializer sample

Merge branch 'fix_commits_dashboard' of https://github.com/jouve/gitlabhq into jouve-fix_commits_dashboard

Conflicts:
	app/views/events/_commit.html.haml

Updated MySQL docs and Ubuntu auto-install script

Fully embrace Ruby 1.9 hash syntax

Features are still expecting the 1.8 syntax, which is fine in this case.

Didn't bother with files in db/, config/, or features/

Consolidate functionality shared between Issue and MergeRequest

ability to preview notes

Fix resque worker becoming paused on restarts

Also adds specs to the two affected classes that would have caught my
dumb mistake.

Any associations, validations, delegates, scopes and methods that
were exactly the same in both Issue and MergeRequest models have been
moved to a new IssueCommonality module (role) that gets included by each
class.

There was actually quite a bit of duplication, because MergeRequests are
basically just specialized Issues.