Don't use $_SERVER['REDIRECT_URL'] (Ticket 11759)

As described in http://bugs.horde.org/ticket/11759, REDIRECT_URL serves no purpose and breaks Horde installations on anything which is not Apache+mod_php - this includes nginx, php on fastcgi and php-fpm.
If the files framework/Controller/lib/Horde/Controller/Request/Mock.php and /MockRequestTest.php need to be updated, too, let me know.