Summary of changes :
- 'maxconn' server parameter to do per-server session limitation
- queueing to support non-blocking session limitation
- fixed removal of cookies for cookie-less servers such as backup servers
- two separate wait queues for expirable and non-expirable tasks provide
better performance with lots of sessions.
- some code cleanups and performance improvements
- made state dumps a bit more verbose
- fixed missing checks for NULL srv in dispatch mode
- load balancing on backup servers was not possible in source hash mode.
- two session flags shared the same bit, but fortunately they were not
compatible.
