The patch that fixed the review group user resource links broke when a

user was a member of more than one group (which is a likely occurance).

This was because we were using a model_parent_key that was a many-to-

many field (and therefore the reverse relation was not unique),

resulting in a MultipleObjectsReturned exception. This has been fixed

by customizing how we retrieve the parent object IDs.

Ran unit tests.