!act,doc,rem,tes 3823 remove deprecated Props methods

- rewrite deprecated usages to their recommended counterparts
- TestActorRef now verifies mailbox requirements
- CallingThreadMailbox now exposes proper messageQueue type for
  inspection

akka-testkit/src/main/scala/akka/testkit/CallingThreadDispatcher.scala

@@ -320,6 +320,12 @@ class CallingThreadMailbox(_receiver: akka.actor.Cell, val mailboxType: MailboxT
     }
   }
 
+  /**
+   * This is only a marker to be put in the messageQueue’s stead to make error
+   * messages pertaining to violated mailbox type requirements less cryptic.
+   */
+  override val messageQueue: MessageQueue = q.get
+
   override def enqueue(receiver: ActorRef, msg: Envelope): Unit = q.get.enqueue(receiver, msg)
   override def dequeue(): Envelope = throw new UnsupportedOperationException("CallingThreadMailbox cannot dequeue normally")
   override def hasMessages: Boolean = q.get.hasMessages