Fix DoesNotExist when non admin visits /admin

SitePermission objects are only added when staff users are created.  If a non admin user (with no manually assigned site permissions) visits the admin a DoesNotExist is raised since no site permissions exist for the user.  Therefore the templatetags logic should only run if the user is staff.
Resolve race condition in conf.settings
Added failing settings race condition test
Simpler fix for race condition in settings
Reorder and add comments to settings test
Merge branch 'master' into settings_threading
Overwrite settings cache when loading from DB
Clear DB settings after test run
Isolate connection hack
Formatting
set_slug now save itself
set_slug now saves itself
Merge branch 'drag-slug-fix' of https://github.com/dustinrb/mezzanine into drag-slug-fix

Conflicts:
	mezzanine/pages/models.py
Remove the requirement for searchable models to subclass Displayable.
Handle installing initial data with Django 1.7's syncdb signals. Closes #1123.
Merge
Added Dustin Broderick to AUTHORS.
Remove redundant page save in slug tests.
Merge
Slightly faster settings loader.