File based cache

So file based alternative for cache in trunk

To test, add in your civicrm.setting.php
define ('CIVICRM_DB_CACHE_CLASS', 'SerializeCache');

http://forum.civicrm.org/index.php/topic,26408.0.html

Problem identified: if mixing drush and web, the cache files (in template_c) got different owners, and you got errors down the road (eg. when trying to clear a cache that was created by the other side.