public function logout()
 {
     $so = Client_Session::getInstance();
     $this->_id = null;
     $so->register('user_id', null, false);
     $this->_data = null;
 }
 protected function saveSessionVar($varname, $value = null)
 {
     $client_session = Client_Session::getInstance();
     if ($value === null) {
         $value = $this->{$varname};
     }
     $svar = $client_session->get($this->ns . $this->_session_var);
     $svar[$varname] = $value;
     $client_session->register($this->ns . $this->_session_var, $svar, false);
 }