Add Single Sign Out/In support

[xiangzhai]

phpCAS supports Single Sign Out when, for example, logout from WordPress, then phpBB3 need to logout automatically.

So I just added

if ($this->user->data['username'] == 'Anonymous') {                        
            $_SESSION['phpBBCAS'] = true;                                          
            $result = $this->auth->login('', '');                                  
        } else {                                                                   
            if (!array_key_exists('phpCAS', $_SESSION))                            
                $this->user->session_kill();                                       
        }

in event/cas_login_listener.php to support single sign out/in.

[xiangzhai]

bring in new Login with DB issue... fixing