Reduce sql queries for groupname tests. (STUD-1039)

Conflicts:
	cms/djangoapps/auth/authz.py
In OpenEndedModule latest_score and all_score calculate sum of rubric scores every time for ML grading.
ORA-72
Merge pull request #1906 from edx/hotfix/2013-12-10

Hotfix/2013 12 10