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/Dispatcher.scala

@@ -4,7 +4,7 @@
 
 package akka.dispatch
 
-import akka.event.EventHandler
+import akka.event.Logging.Warning
 import java.util.concurrent.atomic.AtomicReference
 import java.util.concurrent.{ TimeUnit, ExecutorService, RejectedExecutionException, ConcurrentLinkedQueue }
 import akka.actor.{ ActorCell, ActorKilledException }
@@ -95,7 +95,7 @@ class Dispatcher(
       executorService.get() execute invocation
     } catch {
       case e: RejectedExecutionException ⇒
-        app.eventHandler.warning(this, e.toString)
+        app.mainbus.publish(Warning(this, e.toString))
         throw e
     }
   }
@@ -122,7 +122,7 @@ class Dispatcher(
         } catch {
           case e: RejectedExecutionException ⇒
             try {
-              app.eventHandler.warning(this, e.toString)
+              app.mainbus.publish(Warning(this, e.toString))
             } finally {
               mbox.setAsIdle()
             }