Added AutoFillFastCache option

Allow the fast cache to be (re-)filled automatically using information in the slow cache, without having to enable the AutoRefreshFastCache option, which refreshes the cache entries on EVERY request, causing a lot of expensive writes and removes cache entry hit count statistics.

Also see:
http://framework.zend.com/issues/browse/ZF-8431
http://www.fabrizio-branca.de/magento-zend-frameworks-twolevels-cache-backend-mess.html
http://blog.stoeckl.de/post/11996239388/how-to-fix-two-levels-cache-in-zend-framework
http://framework.zend.com/issues/browse/ZF-8431