Idea: ContainerBuilder: avoid fopen if file is in opcode cache

Bored at school I got an idea to avoid touching disk for PHP 5.5.11+. It relies on undocumented function opcache_is_script_cached (http://stackoverflow.com/questions/23229849/opcache-is-script-cached-function-in-php5-5-11).

Not sure how to solve the atomicity. We may use `@include` and check return value for `FALSE`.

 
Not sure if I am correct but I got to [zend_fopen_wrapper](https://github.com/php/php-src/blob/9a969fdd3b8f4af2b8f36dfbb5aa26f8630ae4f5/Zend/zend.c#L348), is that the function that ultimately loads the script?