Deprecate actorFor in favor of ActorSelection, see #3074

* Deprecate all actorFor methods
* resolveActorRef in provider
* Identify auto receive message
* Support ActorPath in actorSelection
* Support remote actor selections
* Additional tests of actor selection
* Update tests (keep most actorFor tests)
* Update samples to use actorSelection
* Updates to documentation
* Migration guide, including motivation

akka-docs/rst/scala/code/docs/testkit/TestkitDocSpec.scala

@@ -208,10 +208,13 @@ class TestkitDocSpec extends AkkaSpec with DefaultTimeout with ImplicitSender {
 
   "demonstrate probe watch" in {
     import akka.testkit.TestProbe
-    val target = system.actorFor("/buh")
+    val target = system.actorOf(Props(new Actor {
+      def receive = Actor.emptyBehavior
+    }))
     //#test-probe-watch
     val probe = TestProbe()
     probe watch target
+    target ! PoisonPill
     probe.expectMsgType[Terminated].actor must be(target)
     //#test-probe-watch
   }