Fixed #15707 -- Made the GIS feed compatible to the class based feeds and...

Fixed #15707 -- Made the GIS feed compatible to the class based feeds and introduced a little helper view that works like the previous feed view in the syndication app which was removed in r15976.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16540 bcc190cf-cafb-0310-a4f2-bffc1f526a37