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/ThreadPoolBuilder.scala

@@ -9,7 +9,7 @@ import java.util.concurrent._
 import atomic.{ AtomicLong, AtomicInteger }
 import ThreadPoolExecutor.CallerRunsPolicy
 import akka.util.Duration
-import akka.event.EventHandler
+import akka.event.Logging.{ Warning, Error }
 import akka.AkkaApplication
 
 object ThreadPoolConfig {
@@ -227,10 +227,10 @@ class BoundedExecutorDecorator(val app: AkkaApplication, val executor: ExecutorS
       })
     } catch {
       case e: RejectedExecutionException ⇒
-        app.eventHandler.warning(this, e.toString)
+        app.mainbus.publish(Warning(this, e.toString))
         semaphore.release
       case e: Throwable ⇒
-        app.eventHandler.error(e, this, e.getMessage)
+        app.mainbus.publish(Error(e, this, e.getMessage))
         throw e
     }
   }