http: Set _dumped=false initially

The better to keep the IncomingMessage class isomorphic and avoid
creating additional hidden classes.

lib/http.js

@@ -314,6 +314,10 @@ function IncomingMessage(socket) {
 
   // flag for backwards compatibility grossness.
   this._consuming = false;
+
+  // flag for when we decide that this message cannot possibly be
+  // read by the user, so there's no point continuing to handle it.
+  this._dumped = false;
 }
 util.inherits(IncomingMessage, Stream.Readable);