[1.2.X] Fixed #13631 -- Made sure that max_length and min_length are retained...

[1.2.X] Fixed #13631 -- Made sure that max_length and min_length are retained as attributes on form fields. Thanks to mila for the report.

Backport of r15194 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15195 bcc190cf-cafb-0310-a4f2-bffc1f526a37