[1.2.X] Fixed #14027 -- Ensure that reverse() raises an exception when you try...

[1.2.X] Fixed #14027 -- Ensure that reverse() raises an exception when you try to reverse None. Thanks to Alex for the report and patch.

Backport of r13499 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13500 bcc190cf-cafb-0310-a4f2-bffc1f526a37