=per #3933 Correction of seq number logic for persistent channel

* Problem when using PersistentChannel from Processor
* When the seq numbers of the sending processor and the seq numbers
  of the PersistentChannel was out of sync the PersistentChannel
  did not de-duplicate confirmed deliveres that were resent by
  the processor.
* There is a hand-off in the RequestWriter that confirms the
  Processor seq number, and therefore the seq number of the
  RequestWriter must be used in the ConfirmablePersistent from
  the RequestReader
* More tests, covering this scenario

akka-contrib/src/multi-jvm/scala/akka/contrib/pattern/ClusterSingletonManagerSpec.scala

@@ -285,10 +285,8 @@ class ClusterSingletonManagerSpec extends MultiNodeSpec(ClusterSingletonManagerS
       val p = TestProbe()
       within(5.seconds) {
         awaitAssert {
-          println("#Ping")
           system.actorSelection("/user/consumerProxy").tell(Ping, p.ref)
           p.expectMsg(1.second, Pong)
-          println("#Pong")
         }
       }
       // then send the real message