[1.0.X] The tests added in r9185 were altering the test environment in bad

ways. Fixed this with proper setUp() and tearDown() methods.

Backport of r9200 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9203 bcc190cf-cafb-0310-a4f2-bffc1f526a37