Do a redirect if user presses the prev. step button. The rest of this
        is super'd from FormWizard.

def post(self, *args, **kwargs):
        """
        Do a redirect if user presses the prev. step button. The rest of this
        is super'd from FormWizard.
        """
        prev_step = self.request.POST.get('wizard_prev_step', None)
        if prev_step and prev_step in self.get_form_list():
            self.storage.current_step = prev_step
            return redirect(self.url_name, step=prev_step)
        return super(NamedUrlWizardView, self).post(*args, **kwargs)