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.