Merge pull request #1704 from edx/release-hotfix-2013-11-15

merge 2013-11-15 hotfix branch to master

common/lib/xmodule/xmodule/open_ended_grading_classes/peer_grading_service.py

 import json
 import logging
 
-from .grading_service_module import GradingService
+from .grading_service_module import GradingService, GradingServiceError
 
 log = logging.getLogger(__name__)
 
 
-class GradingServiceError(Exception):
-    pass
-
-
 class PeerGradingService(GradingService):
     """
     Interface with the grading controller for peer grading