Java docs and sample of durable mailbox, see #2761

* Added abstract class DurableMessageQueueWithSerialization
(cherry picked from commit 49720e8cd09243ffea9f02c245e0053c126bf555)

akka-docs/rst/java/code/docs/actor/mailbox/MyDurableMailboxDocSpec.scala

@@ -0,0 +1,31 @@
+/**
+ * Copyright (C) 2009-2013 Typesafe Inc. <http://www.typesafe.com>
+ */
+package docs.actor.mailbox
+
+import akka.actor.mailbox.DurableMailboxSpec
+
+object MyDurableMailboxDocSpec {
+  val config = """
+    MyStorage-dispatcher {
+      mailbox-type = docs.actor.mailbox.MyDurableMailboxType
+    }
+    """
+}
+
+class MyDurableMailboxDocSpec extends DurableMailboxSpec("MyStorage", MyDurableMailboxDocSpec.config) {
+  override def atStartup() {
+  }
+
+  override def afterTermination() {
+  }
+
+  "MyDurableMailbox (Java)" must {
+    "deliver a message" in {
+      val actor = createMailboxTestActor()
+      implicit val sender = testActor
+      actor ! "hello"
+      expectMsg("hello")
+    }
+  }
+}