[1.2.X] Fixed #8975 -- documented related order methods -- thanks to Leo for...

[1.2.X] Fixed #8975 -- documented related order methods -- thanks to Leo for the report and dwillis for the initial patch.

Backport of r14848 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14849 bcc190cf-cafb-0310-a4f2-bffc1f526a37