Fixed #14655 -- Made formsets iterable. This allows a slightly more natural iteration API (`for form in formsets`), and allows you to easily override the form rendering order. Thanks to Kent Hauser for the suggestion and patch.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14986 bcc190cf-cafb-0310-a4f2-bffc1f526a37