[1.1.X] Fixed #12217: Documented the fact that serving flatpages from the...

[1.1.X] Fixed #12217: Documented the fact that serving flatpages from the flatpage middleware does not apply view middleware methods. Backport of [12671] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12672 bcc190cf-cafb-0310-a4f2-bffc1f526a37