[1.2.X] Fixed #14156 -- Modified the way CSRF protection is applied to...

[1.2.X] Fixed #14156 -- Modified the way CSRF protection is applied to flatpages so that the flatpage middleware doesn't cause all POSTs resulting in 404s to turn into 403s. Thanks to patrys for the report.

Backport of r13641 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@13643 bcc190cf-cafb-0310-a4f2-bffc1f526a37