Fixed #14504 -- Corrected the way object_list is used in ListView to avoid...

Fixed #14504 -- Corrected the way object_list is used in ListView to avoid overwriting context. Includes improved usage of unittest2 assertions. Thanks to Łukasz Rekucki for the final patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14372 bcc190cf-cafb-0310-a4f2-bffc1f526a37