[1.2.X] Fixed #14252 - django.contrib.flatpages unit tests assume default...

[1.2.X] Fixed #14252 - django.contrib.flatpages unit tests assume default value for settings.LOGIN_URL

Thanks to pmclanahan for report and patch.

Backport of [13851] from trunk

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13853 bcc190cf-cafb-0310-a4f2-bffc1f526a37