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/dispatch/Mailbox.scala

@@ -12,6 +12,7 @@ import akka.actor.{ ActorContext, ActorCell }
 import java.util.concurrent._
 import atomic.{ AtomicInteger, AtomicReferenceFieldUpdater }
 import annotation.tailrec
+import akka.event.Logging.Error
 
 class MessageQueueAppendFailedException(message: String, cause: Throwable = null) extends AkkaException(message, cause)
 
@@ -205,7 +206,7 @@ abstract class Mailbox(val actor: ActorCell) extends AbstractMailbox with Messag
       }
     } catch {
       case e ⇒
-        actor.app.eventHandler.error(e, this, "exception during processing system messages, dropping " + SystemMessage.size(nextMessage) + " messages!")
+        actor.app.mainbus.publish(Error(e, this, "exception during processing system messages, dropping " + SystemMessage.size(nextMessage) + " messages!"))
         throw e
     }
   }