+str #15588,#17229 Java 6 Synchronous File Sink / Source

These are synchronous implementations, because we need to be Java 6
  compatible while developing on 2.3.x. However asynchronous
  implementations using AsynchronousFileChannel will come soon for JDK7
  users.

+ ActorPublisher/Subscriber now manage stopping of the actor
+ added documentation on configuring dispatcher for File IO
+ properly handle if source file does not exist
+ file sink / source come with default io dispatcher
> verified no actors are leaking
> exceptions are caught and onErrored properly
+ moved files to akka.stream.io
+ Added OutputStreamSink and InputStreamSource

akka-stream/src/main/scala/akka/stream/impl/ActorFlowMaterializerImpl.scala

@@ -27,7 +27,8 @@ import scala.concurrent.{ Await, ExecutionContextExecutor }
 /**
  * INTERNAL API
  */
-private[akka] case class ActorFlowMaterializerImpl(override val settings: ActorFlowMaterializerSettings,
+private[akka] case class ActorFlowMaterializerImpl(override val system: ActorSystem,
+                                                   override val settings: ActorFlowMaterializerSettings,
                                                    dispatchers: Dispatchers,
                                                    supervisor: ActorRef,
                                                    flowNameCounter: AtomicLong,
@@ -244,6 +245,13 @@ private[akka] object StreamSupervisor {
   def props(settings: ActorFlowMaterializerSettings): Props = Props(new StreamSupervisor(settings))
 
   final case class Materialize(props: Props, name: String) extends DeadLetterSuppression
+
+  /** Testing purpose */
+  final case object GetChildren
+  /** Testing purpose */
+  final case class Children(children: Set[ActorRef])
+  /** Testing purpose */
+  final case object StopChildren
 }
 
 private[akka] class StreamSupervisor(settings: ActorFlowMaterializerSettings) extends Actor {
@@ -255,6 +263,8 @@ private[akka] class StreamSupervisor(settings: ActorFlowMaterializerSettings) ex
     case Materialize(props, name) ⇒
       val impl = context.actorOf(props, name)
       sender() ! impl
+    case GetChildren  ⇒ sender() ! Children(context.children.toSet)
+    case StopChildren ⇒ context.children.foreach(context.stop)
   }
 }