[1.2.X] Fixed #2283 (again) - comment form templates don't validate as XHTML

Thanks to hjoreteg/thejaswi_puthraya for the report and patch.

Backport of [13855] from trunk

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13856 bcc190cf-cafb-0310-a4f2-bffc1f526a37