[1.2.X] Properly handle the fact that lists are mutable when trying to...

[1.2.X] Properly handle the fact that lists are mutable when trying to maintain state in a test.  Backport of [14429].

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14430 bcc190cf-cafb-0310-a4f2-bffc1f526a37