[1.2.X] Fixed #15055 -- added information about (and an example of) the...

[1.2.X] Fixed #15055 -- added information about (and an example of) the csrf_token template tag to the forms documentation. Thanks to sneakyness for the report and bpeschier for the draft patch.

Backport of [15445] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15446 bcc190cf-cafb-0310-a4f2-bffc1f526a37