[1.3.X] Changed utils/decorators.py tests to use RequestFactory

Backport of [16272] from trunk. Backported to make the backport of a
bugfix (regression) easier.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.3.X@16278 bcc190cf-cafb-0310-a4f2-bffc1f526a37