Short Circuit WIP

- When binding a short-circuited producer, save his properties in
the binding so they can be used to revert, when the consumer is
unbound.

- When the consumer is unbound, bind the producer to the bus
(concurrently with the direct binding), remove the direct binding,
then stop the consumer (so there is always at least one subscriber
to the producing module's output channel.

- TODO: Only short circuit if the admin tells us to (via a property).

- TODO: Beef up test case (currently tested by examining log).

- TODO: LocalMessageBus doesn't compile.