[1.3.X] Fixed #16334: Make it quite clear that cache_page's 'cache' argument...

[1.3.X] Fixed #16334: Make it quite clear that cache_page's 'cache' argument refers to the name of a cache in the CACHES setting. Backport of [16815] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.3.X@16816 bcc190cf-cafb-0310-a4f2-bffc1f526a37