[1.0.X] Fixed #10643: fixed the formtools security hash to handle allowed...

[1.0.X] Fixed #10643: fixed the formtools security hash to handle allowed empty forms or forms without changed data. Backport of [10753] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10755 bcc190cf-cafb-0310-a4f2-bffc1f526a37