Fixed #16393 -- FormWizard's cookie storage backend now works with all...

Fixed #16393 -- FormWizard's cookie storage backend now works with all versions of simplejson and the standard library json module.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17014 bcc190cf-cafb-0310-a4f2-bffc1f526a37