[1.2.X] Fixed #15493 - csrf_migration_helper.py parsing fix.

Thanks to 'john' for the patch.

Backport of [15647] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15648 bcc190cf-cafb-0310-a4f2-bffc1f526a37