Generate an APC prefix based on __FILE__

Closes #654

Author: trsteel88

web/app.php

@@ -6,10 +6,8 @@
 $loader = require_once __DIR__.'/../app/bootstrap.php.cache';
 
 // Use APC for autoloading to improve performance.
-// Change 'sf2' to a unique prefix in order to prevent cache key conflicts
-// with other applications also using APC.
 /*
-$apcLoader = new ApcClassLoader('sf2', $loader);
+$apcLoader = new ApcClassLoader(sha1(__FILE__), $loader);
 $loader->unregister();
 $apcLoader->register(true);
 */