http: avoid create difference hidden class

Reviewed-by: Trevor Norris <trev.norris@gmail.com>

lib/_http_incoming.js

@@ -46,6 +46,8 @@ function IncomingMessage(socket) {
   this.socket = socket;
   this.connection = socket;
 
+  this.httpVersionMajor = null;
+  this.httpVersionMinor = null;
   this.httpVersion = null;
   this.complete = false;
   this.headers = {};
@@ -57,6 +59,7 @@ function IncomingMessage(socket) {
 
   this._pendings = [];
   this._pendingIndex = 0;
+  this.upgrade = null;
 
   // request (server) only
   this.url = '';