[1.2.X] Fixed #14999 -- Ensure that filters on local fields are allowed, and...

[1.2.X] Fixed #14999 -- Ensure that filters on local fields are allowed, and aren't caught as a security problem. Thanks to medhat for the report.

Backport of r15139 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15140 bcc190cf-cafb-0310-a4f2-bffc1f526a37