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-actor/src/main/scala/akka/event/EventBus.scala

@@ -48,6 +48,7 @@ trait EventBus {
  */
 trait ActorEventBus extends EventBus {
   type Subscriber = ActorRef
+  protected def compareSubscribers(a: ActorRef, b: ActorRef) = a compareTo b
 }
 
 /**
@@ -254,9 +255,9 @@ trait ActorClassification { self: ActorEventBus with ActorClassifier ⇒
    */
   protected def mapSize: Int
 
-  def publish(event: Event): Unit = mappings.get(classify(event)) match {
-    case null           ⇒
-    case raw: Vector[_] ⇒ raw.asInstanceOf[Vector[ActorRef]] foreach { _ ! event }
+  def publish(event: Event): Unit = {
+    val receivers = mappings.get(classify(event))
+    if (receivers ne null) receivers foreach { _ ! event }
   }
 
   def subscribe(subscriber: Subscriber, to: Classifier): Boolean = associate(to, subscriber)