Validate form.
        Return True if Django validates the form, the username obeys the parameters, and passwords match.
        Return False otherwise.

def is_valid(self):
        ''' Validate form.
        Return True if Django validates the form, the username obeys the parameters, and passwords match.
        Return False otherwise.
        '''
        if not super(DeleteUserForm, self).is_valid():
            return False
        if self.user == self.request.user:
            self._errors["__all__"] = self.error_class([MESSAGES['SELF_DELETE']])
            return False
        return True