=str: various minor cleanups

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

@@ -0,0 +1,23 @@
+/**
+ * Copyright (C) 2015 Typesafe Inc. <http://www.typesafe.com>
+ */
+package akka.stream.impl
+
+import akka.stream._
+import akka.stream.impl.StreamLayout.Module
+
+/**
+ * INTERNAL API
+ */
+private[stream] trait FlowModule[In, Out, Mat] extends StreamLayout.Module {
+  override def replaceShape(s: Shape) =
+    if (s == shape) this
+    else throw new UnsupportedOperationException("cannot replace the shape of a FlowModule")
+
+  val inPort = Inlet[In]("Flow.in")
+  val outPort = Outlet[Out]("Flow.out")
+  override val shape = new FlowShape(inPort, outPort)
+
+  override def subModules: Set[Module] = Set.empty
+}
+