fix CTD vs. RepointableRef by swallowing exceptions during send

- it was always intended that tell() (and sendSystemMessage()) shall not
  throw any exceptions
- this is implemented by swallowing in ActorCell
  (suspend/resume/restart/stop/!/sendSystemMessage) and in
  RemoteActorRef (!/sendSystemMessage)
- current implementation uses a normal method, which adds overhead but
  keeps the code in one place (ActorCell.catchingSend); this is a great
  opportunity for making use of macros

akka-actor-tests/src/test/scala/akka/serialization/SerializeSpec.scala

@@ -269,8 +269,8 @@ class VerifySerializabilitySpec extends AkkaSpec(VerifySerializabilitySpec.conf)
     val a = system.actorOf(Props[FooActor])
     Await.result(a ? "pigdog", timeout.duration) must be("pigdog")
 
-    intercept[NotSerializableException] {
-      Await.result(a ? new AnyRef, timeout.duration)
+    EventFilter[NotSerializableException](occurrences = 1) intercept {
+      a ! (new AnyRef)
     }
     system stop a
   }