[1.2.X] Fixed #13218 -- Ensure that syndicated content served over HTTPS uses...

[1.2.X] Fixed #13218 -- Ensure that syndicated content served over HTTPS uses https:// links by default. Thanks to schaefer for the report, and Ben Firshman for the patch.

Backport of r14007 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14010 bcc190cf-cafb-0310-a4f2-bffc1f526a37