Fixed several memory and thread leaks. See #1404

* Dispatchers need Scheduler to be able to shutdown themselves. Stop Scheduler after dispatchers.
* Changed CallingThreadDispatcher global object to Extension, since it holds map of references to mailboxes. Will be GC:ed when system is GC:ed.
* Made testActor lazy, since it is not used in all tests, and it creates CallingThreadDispatcher.
* Activated some java tests that were not running
* Many tests were not stopping created ActorSystems. VERY IMPORTANT TO STOP ActorSystem in tests. Use AkkaSpec as much as possible.
* Used profiler to verify (and find) dangling ActorSystemImpl and threads from dispatchers.
* FutureSpec creates ForkJoinPool threads that are not cleared, but number of threads don't grow so it's not a problem.

akka-actor-tests/src/test/scala/akka/util/JavaDurationSpec.scala

@@ -0,0 +1,8 @@
+/**
+ *  Copyright (C) 2009-2011 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.util
+
+import org.scalatest.junit.JUnitSuite
+
+class JavaDurationSpec extends JavaDuration with JUnitSuite