Fixed #8253: fixed xmlns regression for Atom feeds, and in the process added a...

Fixed #8253: fixed xmlns regression for Atom feeds, and in the process added a hook for adding attributes specifically on the root <rss> element (for RSS feeds only, of course). Patch by Justin Bronn.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@8331 bcc190cf-cafb-0310-a4f2-bffc1f526a37