apcu module mock

[APCU](https://github.com/krakjoe/apcu) module.

Will work on Ubuntu 13.04/ 13.10 as there is a package `php5-apcu` now.

Still need look at Ubuntu 12.04. dependencies that may be broken at the moment (current up-to-date host can not install pcre dev due to version conflict; need to fall back to dpkg to fix the broken dependency description of an ubuntu version alias).