Memcache Performance Improvements

This is a new experimental technique for speeding up database queries to improve performance for searches and retrieving products and related data. All ecommerce sites will benefit from this, in particular auto parts sites which tend to have the largest number of products to query against. It is turned off by default.

To use this feature, go into Site Settings and tick Memcache caching support. Leave Default cache expiration seconds: blank for the default (86400) or set to zero (0) to never expire. 

If you set it to zero you'll need to manually refresh the cache via this program. 

NB After changing any site setting values please run this program again.