first step: sanitize ActorPath interface

- remove references to ActorSystem
- make ChildActorPath light-weight (name & parent plus tailrec methods
  for traversing towards root, e.g. toString)
- string rep is full URI always (akka://system-name@host:port/user/bla)

akka-actor/src/main/scala/akka/remote/RemoteInterface.scala

@@ -28,10 +28,10 @@ object RemoteAddress {
 
 object LocalOnly extends RemoteAddress(0, "local")
 
-case class RemoteAddress private[akka] (port: Int, hostname: String) {
+case class RemoteAddress private[akka] (port: Int, hostname: String) extends Address {
+  def protocol = "akka"
   @transient
-  override lazy val toString = "" + hostname + ":" + port
-
+  lazy val hostPort = hostname + ":" + port
 }
 
 class RemoteException(message: String) extends AkkaException(message)