Flow timeout code keeps track of thread module running detect, and
fails (hard) if it doesn't find it.
This changeset retrieves the global g_detect_disabled and passes
it to the timeout handling code during setup.
Major redesign of the flow engine. Remove the flow queues that turned
out to be major choke points when using many threads. Flow manager now
walks the hash table directly. Simplify the way we get a new flow in
case of emergency.