improve DeadLetter reporting

(since I know now what’s causing these Jenkins failures ;-) )

- include recipient in DeadLetter
- include recipient in calls to enqueue/systemEnqueue
- move DeadLetterMailbox to ActorSystem (saves some space, too)
- hook up DeadLetterMailbox so it sends DeadLetters to app.deadLetters,
  which publishes them on the eventStream
- subscribe TestEventListener to DeadLetter and turn it into Warning

The generated warnings about ChildTerminated are very much correct, they
remind us that we still need to fix supervisor.stop() to await all
children’s death before actually committing suicide.

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

@@ -7,7 +7,7 @@ import akka.AkkaException
 import java.util.{ Comparator, PriorityQueue }
 import akka.util._
 import java.util.Queue
-import akka.actor.{ ActorContext, ActorCell }
+import akka.actor.{ ActorContext, ActorCell, ActorRef }
 import java.util.concurrent._
 import atomic.{ AtomicInteger, AtomicReferenceFieldUpdater }
 import annotation.tailrec
@@ -217,7 +217,7 @@ trait MessageQueue {
   /*
    * These method need to be implemented in subclasses; they should not rely on the internal stuff above.
    */
-  def enqueue(handle: Envelope)
+  def enqueue(receiver: ActorRef, handle: Envelope)
 
   def dequeue(): Envelope
 
@@ -230,7 +230,7 @@ trait SystemMessageQueue {
   /**
    * Enqueue a new system message, e.g. by prepending atomically as new head of a single-linked list.
    */
-  def systemEnqueue(message: SystemMessage): Unit
+  def systemEnqueue(receiver: ActorRef, message: SystemMessage): Unit
 
   /**
    * Dequeue all messages from system queue and return them as single-linked list.
@@ -243,7 +243,7 @@ trait SystemMessageQueue {
 trait DefaultSystemMessageQueue { self: Mailbox ⇒
 
   @tailrec
-  final def systemEnqueue(message: SystemMessage): Unit = {
+  final def systemEnqueue(receiver: ActorRef, message: SystemMessage): Unit = {
     assert(message.next eq null)
     if (Mailbox.debug) println(actor + " having enqueued " + message)
     val head = systemQueueGet
@@ -256,7 +256,7 @@ trait DefaultSystemMessageQueue { self: Mailbox ⇒
     message.next = head
     if (!systemQueuePut(head, message)) {
       message.next = null
-      systemEnqueue(message)
+      systemEnqueue(receiver, message)
     }
   }
 
@@ -270,7 +270,7 @@ trait DefaultSystemMessageQueue { self: Mailbox ⇒
 }
 
 trait UnboundedMessageQueueSemantics extends QueueBasedMessageQueue {
-  final def enqueue(handle: Envelope): Unit = queue add handle
+  final def enqueue(receiver: ActorRef, handle: Envelope): Unit = queue add handle
   final def dequeue(): Envelope = queue.poll()
 }
 
@@ -278,7 +278,7 @@ trait BoundedMessageQueueSemantics extends QueueBasedMessageQueue {
   def pushTimeOut: Duration
   override def queue: BlockingQueue[Envelope]
 
-  final def enqueue(handle: Envelope) {
+  final def enqueue(receiver: ActorRef, handle: Envelope) {
     if (pushTimeOut.length > 0) {
       queue.offer(handle, pushTimeOut.length, pushTimeOut.unit) || {
         throw new MessageQueueAppendFailedException("Couldn't enqueue message " + handle + " to " + toString)