make remote lookup work

- create RemoteActorRef in actorFor
- simplify send/receive because Futures/Exceptions do not go over the
  wire anymore
- add RemoteCommunicationSpec which uses two ActorSystems communicating
  in the same JVM via TCP socket

akka-actor/src/main/scala/akka/dispatch/AbstractDispatcher.scala

@@ -53,6 +53,7 @@ object SystemMessage {
  * ➡➡➡ NEVER SEND THE SAME SYSTEM MESSAGE OBJECT TO TWO ACTORS ⬅⬅⬅
  */
 sealed trait SystemMessage extends PossiblyHarmful {
+  @transient
   var next: SystemMessage = _
 }
 case class Create() extends SystemMessage // send to self from Dispatcher.register