* Callbacks for processTribC::spawnProcess() now return the new process'
  first thread's ID as their "sourceId" member.
* Replaced timerStreamC::requestS with a new request object type that properly
  contains a zrequest::headerS object within itself.
  ^ Cleaned up Timer Stream macros.
  ^ Unified Timer Stream request infrastructure.
* Fixed a bug due to overlapping variable name precedence in
  timerStreamC::createOneshotEvent().
* Defined 4 USER<0-3> callback queues for threads to use for posting custom
  messages to one another.