[1.2.X] Fixed #15260 -- Ensured that CACHE_MIDDLEWARE_ANONYMOUS_ONLY is...

[1.2.X] Fixed #15260 -- Ensured that CACHE_MIDDLEWARE_ANONYMOUS_ONLY is effective with the cache_page decorator, not only the middleware. Thanks to brodie for report and draft patch.

Backport of r15559 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15560 bcc190cf-cafb-0310-a4f2-bffc1f526a37