LUN-943 -- Make sure the groups change list doesn't contain duplicate entries by making a distinct on the returned queryset
Use the reciever decorator for making the singal handlers more readable
Break the unit tests in multiple classes for better readability
Do proper cleanup when deleting a group that a role is built on top of
A more readable/understandable comment
Improve the speed at which auto-generated groups get updated by only running the signal handler for post_* actions
Remove code that was handling an exception that would have never been raised
Merge pull request #13 from pbs/LUN-943

LUN-943 -- Make sure the groups change list doesn't contain duplicate entries by making a distinct on the returned queryset