Introduce parental supervision, BUT TESTS ARE STILL FAILING

- every actor is now supervised, where the root of the tree is
  app.guardian, which has its supervisor field set to a special ActorRef
  obtained from provider.theOneWhoWalksTheBubblesOfSpaceTime (this name
  is meant to indicate that this ref is outside of the universe, cf.
  Michio Kaku)
- changed all tests to obtain specially supervised children (i.e. not
  top-level) via (supervisor ? Props).as[ActorRef].get
- add private[akka] ScalaActorRef.sendSystemMessage for sending
  Supervise()
- everything routing or remote is broken wrt. supervision, as that was
  not “properly” implemented to begin with, will be tackled after
  app/supervision/eventbus/AkkaSpec are stabilized enough

akka-remote/src/main/scala/akka/remote/NetworkEventStream.scala

@@ -64,8 +64,10 @@ class NetworkEventStream(val app: AkkaApplication) {
 
   import NetworkEventStream._
 
+  // FIXME: check that this supervision is correct
   private[akka] val channel = app.provider.actorOf(
-    Props[Channel].copy(dispatcher = app.dispatcherFactory.newPinnedDispatcher("NetworkEventStream")), Props.randomAddress, systemService = true)
+    Props[Channel].copy(dispatcher = app.dispatcherFactory.newPinnedDispatcher("NetworkEventStream")),
+    app.guardian, Props.randomAddress, systemService = true)
 
   /**
    * Registers a network event stream listener (asyncronously).