remove ActorRef.stop()

- replace ActorRef.stop() by ActorRefFactory.stop(child) everywhere
- ActorCell “optimizes” this to remove the child from its childrenRefs
  in order to allow immediate recycling of the name
- the lost soul must have a place, for which the Locker has been
  created, where Davy Jones will happily rebind the soul to his ship
  (i.e. set “parent” to the locker to avoid mem leak) and periodically
  revisit it (.stop(), in case of that being lost in comm failure,
  similar .watch() to re-check liveness)

akka-docs/scala/code/ActorDocSpec.scala

@@ -40,7 +40,7 @@ class FirstActor extends Actor {
           case DoIt(msg) ⇒
             val replyMsg = doSomeDangerousWork(msg)
             sender ! replyMsg
-            self.stop()
+            context.stop(self)
         }
         def doSomeDangerousWork(msg: ImmutableMessage): String = { "done" }
       })) ! m
@@ -143,7 +143,7 @@ class ActorDocSpec extends AkkaSpec(Map("akka.loglevel" -> "INFO")) {
     //#import-context
 
     val first = system.actorOf(Props(new FirstActor))
-    first.stop()
+    system.stop(first)
 
   }
 
@@ -169,7 +169,7 @@ class ActorDocSpec extends AkkaSpec(Map("akka.loglevel" -> "INFO")) {
     system.eventStream.unsubscribe(testActor)
     system.eventStream.publish(TestEvent.UnMute(filter))
 
-    myActor.stop()
+    system.stop(myActor)
   }
 
   "creating actor with constructor" in {
@@ -182,7 +182,7 @@ class ActorDocSpec extends AkkaSpec(Map("akka.loglevel" -> "INFO")) {
     val myActor = system.actorOf(Props(new MyActor("...")))
     //#creating-constructor
 
-    myActor.stop()
+    system.stop(myActor)
   }
 
   "creating actor with Props" in {
@@ -192,7 +192,7 @@ class ActorDocSpec extends AkkaSpec(Map("akka.loglevel" -> "INFO")) {
     val myActor = system.actorOf(Props[MyActor].withDispatcher(dispatcher), name = "myactor")
     //#creating-props
 
-    myActor.stop()
+    system.stop(myActor)
   }
 
   "using ask" in {
@@ -214,7 +214,7 @@ class ActorDocSpec extends AkkaSpec(Map("akka.loglevel" -> "INFO")) {
     val result: Option[Int] = for (x ← (myActor ? 3).as[Int]) yield { 2 * x }
     //#using-ask
 
-    myActor.stop()
+    system.stop(myActor)
   }
 
   "using receiveTimeout" in {