Fixed #9473: FormWizard now works with NullBooleanFields. As a bonus, we now have the beginnings of a test suite for FormWizard. Thanks, Keith Bussell.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@10316 bcc190cf-cafb-0310-a4f2-bffc1f526a37