Cosmetic changes to common_redirect, clientError, serverError

Since these functions exit (or throw exception) after running, there
is no need to have a 'return' statement or similar afterwards.

plugins/CasAuthentication/actions/caslogin.php

@@ -39,14 +39,12 @@ class CasloginAction extends Action
             if (!$user) {
                 // TRANS: Server error displayed when trying to log in with incorrect username or password.
                 $this->serverError(_m('Incorrect username or password.'));
-                return;
             }
 
             // success!
             if (!common_set_user($user)) {
                 // TRANS: Server error displayed when login fails in CAS authentication plugin.
                 $this->serverError(_m('Error setting user. You are probably not authorized.'));
-                return;
             }
 
             common_real_login(true);