Symfony2: change APC to xcache-Collection of common programming errors

Because a Bug in APC, i had to use another Cache-Drive. I removed APC and installed xcache. config.php says Your configuration looks good to run Symfony.

I got the following error on request:

PHP Fatal error:  Uncaught exception 'RuntimeException' with message 'Unable to use ApcClassLoader as APC is not enabled.' in /var/.../app/bootstrap.php.cache:1039
Stack trace:
#0 /var/.../web/app.php(11): Symfony\\Component\\ClassLoader\\ApcClassLoader->__construct('sf2', Object(Composer\\Autoload\\ClassLoader))
#1 {main}
thrown in /var/...app/bootstrap.php.cache on line 1039

How do I tell Symfony to use xcache instead of APC?