Add php ZendOptimusPlus support.

Zend opensourced their new opcode cache for PHP and will be part of PHP in near future, this adds monitoring for that extension. 

It's similar to phpapc, but simpler, my machine have it running for a day and I think it's good enough.

Examples:

![php_zop_opcache_statistics-day](https://f.cloud.github.com/assets/1033514/401714/9a5b862e-a8e6-11e2-93ae-cb25cf3d57ed.png)
![php_zop_memory-day](https://f.cloud.github.com/assets/1033514/401715/9a640178-a8e6-11e2-9dbb-7e711c146047.png)
![php_zop_key_status-day](https://f.cloud.github.com/assets/1033514/401716/9a8dbfa4-a8e6-11e2-98e9-39b2875a6119.png)
![php_zop_opcache_hitrate-day](https://f.cloud.github.com/assets/1033514/401717/9a9727a6-a8e6-11e2-9f03-eb36f4de9a0b.png)