[1.0.X] Fixed up the tests added for #9779 to run under Python 2.3, which doesn't have set.

Merge of the part of [10392] that applies to the 1.0.X branch.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10393 bcc190cf-cafb-0310-a4f2-bffc1f526a37