[1.0.X] Fixed #9587. Formset.is_valid() now returns True if an invalid form is...

[1.0.X] Fixed #9587. Formset.is_valid() now returns True if an invalid form is marked for deletion. Backport of r10206 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10219 bcc190cf-cafb-0310-a4f2-bffc1f526a37