This class takes care of setting the php session handler to use a custom user
implemented session handler.

The basic functionality is to save all the sessions in a MySQL Database table.

Optional usage is to have a memcache as a write through cache for performance on
read only requests for the session.

This setup is good for loadbalanced and clustered webservers where toss the user
between several servers.

It's also good for virtual clustered environments with GFS as it's a known bug
that the PHP session module can stall several servers while waiting for another
process to releases the lock on the session file.