another round of fixes due to suspend counting, see #2212

- always suspend/resume for Suspend/Resume/Recreate, no matter which
  state the actor is in, to keep the counter balanced
- preRestart failures are logged but otherwise ignored; there’s nothing
  else (apart from terminating the actor) which we could do at that
  point
- preRestart/postRestart exceptions have their own distinguishable
  subtype of ActorKilledException now
- fix some race conditions in tests to make them produce fewer false
  failures
- remove cruft from SupervisorStrategy and add methods which can
  actually be used to implement your own (with proper warning signs)

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

@@ -151,7 +151,7 @@ class CallingThreadDispatcher(
 
   override def suspend(actor: ActorCell) {
     actor.mailbox match {
-      case m: CallingThreadMailbox ⇒ m.suspendSwitch.switchOn
+      case m: CallingThreadMailbox ⇒ m.suspendSwitch.switchOn; m.becomeSuspended()
       case m                       ⇒ m.systemEnqueue(actor.self, Suspend())
     }
   }
@@ -163,11 +163,12 @@ class CallingThreadDispatcher(
         val wasActive = queue.isActive
         val switched = mbox.suspendSwitch.switchOff {
           CallingThreadDispatcherQueues(actor.system).gatherFromAllOtherQueues(mbox, queue)
+          mbox.becomeOpen()
         }
         if (switched && !wasActive) {
           runQueue(mbox, queue)
         }
-      case m ⇒ m.systemEnqueue(actor.self, Resume())
+      case m ⇒ m.systemEnqueue(actor.self, Resume(false))
     }
   }