=str fix sub-upstream cancellation in concatAll

- ActorProcessor terminated eagerly when ConcatAll had just taken up a
  new input stream but not yet received onSubscribe for it

- The ActorProcessor eagerly shuts itself down upon onError and that
  cannot be changed without completely reworking the Pump, so I opted
  for just tracking the outstanding substreamSubscribers that have not
  yet seen OnSubscribe and making them cancel properly when that arrives
  (possibly later).

akka-http-core/src/test/scala/akka/http/impl/engine/client/LowLevelOutgoingConnectionSpec.scala

@@ -348,7 +348,7 @@ class LowLevelOutgoingConnectionSpec extends AkkaSpec("akka.loggers = []\n akka.
   }
 
   class TestSetup {
-    val requests = TestPublisher.manualProbe[HttpRequest]
+    val requests = TestPublisher.manualProbe[HttpRequest]()
     val responses = TestSubscriber.manualProbe[HttpResponse]
     val remoteAddress = new InetSocketAddress("example.com", 80)
 
@@ -357,7 +357,7 @@ class LowLevelOutgoingConnectionSpec extends AkkaSpec("akka.loggers = []\n akka.
 
     val (netOut, netIn) = {
       val netOut = TestSubscriber.manualProbe[ByteString]
-      val netIn = TestPublisher.manualProbe[ByteString]
+      val netIn = TestPublisher.manualProbe[ByteString]()
 
       FlowGraph.closed(OutgoingConnectionBlueprint(remoteAddress, settings, NoLogging)) { implicit b ⇒
         client ⇒

akka-http-core/src/test/scala/akka/http/impl/engine/server/HttpServerSpec.scala

@@ -406,7 +406,7 @@ class HttpServerSpec extends AkkaSpec("akka.loggers = []\n akka.loglevel = OFF")
              |Host: example.com
              |
              |""".stripMarginWithNewline("\r\n"))
-      val data = TestPublisher.manualProbe[ByteString]
+      val data = TestPublisher.manualProbe[ByteString]()
       inside(expectRequest) {
         case HttpRequest(GET, _, _, _, _) ⇒
           responsesSub.sendNext(HttpResponse(entity = HttpEntity.Default(ContentTypes.`text/plain`, 4, Source(data))))
@@ -429,7 +429,7 @@ class HttpServerSpec extends AkkaSpec("akka.loggers = []\n akka.loglevel = OFF")
              |Host: example.com
              |
              |""".stripMarginWithNewline("\r\n"))
-      val data = TestPublisher.manualProbe[ByteString]
+      val data = TestPublisher.manualProbe[ByteString]()
       inside(expectRequest) {
         case HttpRequest(GET, _, _, _, _) ⇒
           responsesSub.sendNext(HttpResponse(entity = HttpEntity.CloseDelimited(ContentTypes.`text/plain`, Source(data))))
@@ -453,7 +453,7 @@ class HttpServerSpec extends AkkaSpec("akka.loggers = []\n akka.loglevel = OFF")
              |Host: example.com
              |
              |""".stripMarginWithNewline("\r\n"))
-      val data = TestPublisher.manualProbe[ChunkStreamPart]
+      val data = TestPublisher.manualProbe[ChunkStreamPart]()
       inside(expectRequest) {
         case HttpRequest(GET, _, _, _, _) ⇒
           responsesSub.sendNext(HttpResponse(entity = HttpEntity.Chunked(ContentTypes.`text/plain`, Source(data))))
@@ -477,7 +477,7 @@ class HttpServerSpec extends AkkaSpec("akka.loggers = []\n akka.loglevel = OFF")
              |Connection: close
              |
              |""".stripMarginWithNewline("\r\n"))
-      val data = TestPublisher.manualProbe[ByteString]
+      val data = TestPublisher.manualProbe[ByteString]()
       inside(expectRequest) {
         case HttpRequest(GET, _, _, _, _) ⇒
           responsesSub.sendNext(HttpResponse(entity = CloseDelimited(ContentTypes.`text/plain`, Source(data))))

akka-http-core/src/test/scala/akka/http/impl/engine/server/HttpServerTestSetupBase.scala

@@ -29,13 +29,13 @@ abstract class HttpServerTestSetupBase {
   implicit def materializer: FlowMaterializer
 
   val requests = TestSubscriber.manualProbe[HttpRequest]
-  val responses = TestPublisher.manualProbe[HttpResponse]
+  val responses = TestPublisher.manualProbe[HttpResponse]()
 
   def settings = ServerSettings(system).copy(serverHeader = Some(Server(List(ProductVersion("akka-http", "test")))))
   def remoteAddress: Option[InetSocketAddress] = None
 
   val (netIn, netOut) = {
-    val netIn = TestPublisher.manualProbe[ByteString]
+    val netIn = TestPublisher.manualProbe[ByteString]()
     val netOut = TestSubscriber.manualProbe[ByteString]
 
     FlowGraph.closed(HttpServerBluePrint(settings, remoteAddress = remoteAddress, log = NoLogging)) { implicit b ⇒

akka-http-core/src/test/scala/akka/http/impl/engine/ws/MessageSpec.scala

@@ -222,7 +222,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
         "for a strict message larger than configured maximum frame size" in pending
         "for a streamed message" in new ServerTestSetup {
           val data = ByteString("abcdefg", "ASCII")
-          val pub = TestPublisher.manualProbe[ByteString]
+          val pub = TestPublisher.manualProbe[ByteString]()
           val msg = BinaryMessage.Streamed(Source(pub))
           netOutSub.request(6)
           pushMessage(msg)
@@ -245,7 +245,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
         "for a streamed message with a chunk being larger than configured maximum frame size" in pending
         "and mask input on the client side" in new ClientTestSetup {
           val data = ByteString("abcdefg", "ASCII")
-          val pub = TestPublisher.manualProbe[ByteString]
+          val pub = TestPublisher.manualProbe[ByteString]()
           val msg = BinaryMessage.Streamed(Source(pub))
           netOutSub.request(7)
           pushMessage(msg)
@@ -278,7 +278,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
         "for a strict message larger than configured maximum frame size" in pending
         "for a streamed message" in new ServerTestSetup {
           val text = "äbcd€fg"
-          val pub = TestPublisher.manualProbe[String]
+          val pub = TestPublisher.manualProbe[String]()
           val msg = TextMessage.Streamed(Source(pub))
           netOutSub.request(6)
           pushMessage(msg)
@@ -310,7 +310,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
           println(half1(0).toInt.toHexString)
           println(half2(0).toInt.toHexString)
 
-          val pub = TestPublisher.manualProbe[String]
+          val pub = TestPublisher.manualProbe[String]()
           val msg = TextMessage.Streamed(Source(pub))
           netOutSub.request(6)
 
@@ -327,7 +327,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
         "for a streamed message with a chunk being larger than configured maximum frame size" in pending
         "and mask input on the client side" in new ClientTestSetup {
           val text = "abcdefg"
-          val pub = TestPublisher.manualProbe[String]
+          val pub = TestPublisher.manualProbe[String]()
           val msg = TextMessage.Streamed(Source(pub))
           netOutSub.request(5)
           pushMessage(msg)
@@ -382,7 +382,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
         s.request(2)
         sub.expectNext(ByteString("123", "ASCII"))
 
-        val outPub = TestPublisher.manualProbe[ByteString]
+        val outPub = TestPublisher.manualProbe[ByteString]()
         val msg = BinaryMessage.Streamed(Source(outPub))
         netOutSub.request(10)
         pushMessage(msg)
@@ -459,7 +459,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
         messageIn.expectComplete()
 
         // sending another message is allowed before closing (inherently racy)
-        val pub = TestPublisher.manualProbe[ByteString]
+        val pub = TestPublisher.manualProbe[ByteString]()
         val msg = BinaryMessage.Streamed(Source(pub))
         pushMessage(msg)
         expectFrameOnNetwork(Opcode.Binary, ByteString.empty, fin = false)
@@ -504,7 +504,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
 
           // sending another message is allowed before closing (inherently racy)
 
-          val pub = TestPublisher.manualProbe[ByteString]
+          val pub = TestPublisher.manualProbe[ByteString]()
           val msg = BinaryMessage.Streamed(Source(pub))
           pushMessage(msg)
           expectFrameOnNetwork(Opcode.Binary, ByteString.empty, fin = false)
@@ -549,7 +549,7 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
         messageInSub.request(10)
 
         // send half a message
-        val pub = TestPublisher.manualProbe[ByteString]
+        val pub = TestPublisher.manualProbe[ByteString]()
         val msg = BinaryMessage.Streamed(Source(pub))
         pushMessage(msg)
         expectFrameOnNetwork(Opcode.Binary, ByteString.empty, fin = false)
@@ -765,11 +765,11 @@ class MessageSpec extends FreeSpec with Matchers with WithMaterializerSpec {
     protected def serverSide: Boolean
     protected def closeTimeout: FiniteDuration = 1.second
 
-    val netIn = TestPublisher.manualProbe[ByteString]
+    val netIn = TestPublisher.manualProbe[ByteString]()
     val netOut = TestSubscriber.manualProbe[ByteString]
 
     val messageIn = TestSubscriber.manualProbe[Message]
-    val messageOut = TestPublisher.manualProbe[Message]
+    val messageOut = TestPublisher.manualProbe[Message]()
 
     val messageHandler: Flow[Message, Message, Unit] =
       Flow.wrap {