[BUG] queue management: wake oldest request in queues

[BUG] queue management: wake oldest request in queues

When a server terminates a connection, the next session in its
own queue was immediately processed. Because of this, if all
server queues are always filled, then no new anonymous request
will be processed. Consider oldest request between global and
server queues to choose from which to pick the request.

An improvement over this will consist in adding a configurable
offset when comparing expiration dates, so that cookie-less
requests can get either less or more priority.