Adds Google App Engine specific memcache drivers for Cache and Storage

Adds Google App Engine specific modifications for Cache and Session Storage.

While the vanilla memcached engines should work for an app running in a live GAE instance, they won't work when running locally and they include calls to methods which GAE does not implement.

Specifically: 
Replace any checks for the Memcached extension with checks of $_SERVER variables to see if we are running under GAE[local SDK does not use the extension].  

Removes calls to addServer[GAE App Engine does not use this feature] or attempts at trying to set a memcached server.