[1.0.X] Fixed #8857 -- Corrected ref in modelforms documentation and added ref...

[1.0.X] Fixed #8857 -- Corrected ref in modelforms documentation and added ref to file upload documentation in form documentation. Thanks Kyle Fox and prairiedogg.

Backport of [10837] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10838 bcc190cf-cafb-0310-a4f2-bffc1f526a37