document Specs2 + TestKit, see #2068, plus fix up broken includes

- include move of doc samples out of akka package also in the
  includecode directives
- fix broken serialization docs, which require one thing in the akka
  package

akka-docs/scala/code/docs/testkit/Specs2DemoSpec.scala

@@ -0,0 +1,34 @@
+package docs.testkit
+
+import org.specs2.mutable.Specification
+import org.specs2.specification.Scope
+
+import akka.actor.{ Props, ActorSystem, Actor }
+import akka.testkit.{ TestKit, ImplicitSender }
+
+class Specs2DemoUnitSpec extends Specification {
+
+  val system = ActorSystem()
+
+  implicit def d2d(d: org.specs2.time.Duration): akka.util.FiniteDuration =
+    akka.util.Duration(d.inMilliseconds, "millis")
+
+  /*
+   * this is needed if different test cases would clash when run concurrently,
+   * e.g. when creating specifically named top-level actors
+   */
+  sequential
+
+  "A TestKit" should {
+    "work properly with Specs2 unit tests" in
+      new TestKit(system) with Scope with ImplicitSender {
+        within(1 second) {
+          system.actorOf(Props(new Actor {
+            def receive = { case x ⇒ sender ! x }
+          })) ! "hallo"
+
+          expectMsgType[String] must be equalTo "hallo"
+        }
+      }
+  }
+}