[DEV-1740] fixed auth_user editing in Django admin and one more bugfix in the livesettings

(cherry picked from commit db27ed730000516b98edc3df149abe129dab6dcc)

Conflicts:
	askbot/deps/livesettings/values.py
[DEV-1740] Switch User to AuthUser in m2m_changed signal connection.
Merge pull request #25 from roverdotcom/DEV-1740

[DEV-1740] Fix 500 error on modifying users from admin.