introducing: MainBus feat. LoggingBus

most tests passing, everything compiling, but docs not updated and nasty
thread-leak preventing me from running the whole test-suite (which is
the reason for this commit: I want to chase down that one first).

- the app.mainbus is classified by Class[_] (currently lookup, will
  possibly change to sub-class-aware) and accepts AnyRef messages
- LoggingBus handles akka.event-handlers from config specially:
  + start them as system services, supervised by SystemGuardian
  + keep their subscriptions in sync when logLevel_= is called
  + send them InitializeLogger(bus) message before subscribing them (so
    they can register for extras like Mute/UnMute)
- two-phased start-up: first phase with actor-less stdout logging, then
  subscription of config loggers, then remove stdout logger (logLevels
  configurable separately)
- MainBusReaper watches registered receivers and unsubscribes them upon
  death (started in phase 2)
- logger factory on Logging object, needs app/bus and log source;
  default instance in app.log

akka-tutorials/akka-tutorial-second/src/main/scala/Pi.scala

@@ -5,7 +5,7 @@
 package akka.tutorial.second
 
 import akka.actor.Actor._
-import akka.event.EventHandler
+import akka.event.Logging
 import System.{ currentTimeMillis ⇒ now }
 import akka.routing.Routing.Broadcast
 import akka.actor.{ Timeout, Channel, Actor, PoisonPill }
@@ -15,6 +15,7 @@ import akka.AkkaApplication
 object Pi extends App {
 
   val app = AkkaApplication()
+  val log = Logging(app, this)
 
   calculate(nrOfWorkers = 4, nrOfElements = 10000, nrOfMessages = 10000)
 
@@ -110,9 +111,9 @@ object Pi extends App {
     master.?(Calculate, Timeout(60000)).
       await.resultOrException match { //wait for the result, with a 60 seconds timeout
         case Some(pi) ⇒
-          app.eventHandler.info(this, "\n\tPi estimate: \t\t%s\n\tCalculation time: \t%s millis".format(pi, (now - start)))
+          log.info("\n\tPi estimate: \t\t{}\n\tCalculation time: \t{} millis", pi, now - start)
         case None ⇒
-          app.eventHandler.error(this, "Pi calculation did not complete within the timeout.")
+          log.error("Pi calculation did not complete within the timeout.")
       }
   }
 }