Check to make sure password fields match.

def clean(self):
        '''Check to make sure password fields match.'''
        data = super(PasswordForm, self).clean()
        if 'new_password' in data:
            if data['new_password'] != data.get('confirm_password', None):
                raise ValidationError(_('Passwords do not match.'))
            if data.get('confirm_password', None) == \
                    data.get('current_password', None):
                raise ValidationError(_('Old password and new password '
                                        'must be different'))
        return data