- move all creation of ActorRefs into the ActorRefProvider (deadLetters,
locker)
- rootPath does not contain remote transport address any longer in order
to start the LocalActorRefProvider before the RemoteTransport; the
transport address is inserted during serialization only, which enables
us later to have more than one transport available for one actor
system (maybe even needed for clustering)
- fix inheritance between DeadLetterActorRef and EmptyLocalActorRef
- document some start-up dependencies by reordering constructor code
- fix remote tests which used self.path for identifying remote actors
(since that no longer includes the remote transport address)
