[fix] handler variable in createServer was global (!)

lib/node-http-proxy.js

@@ -128,7 +128,7 @@ exports.setMaxSockets = function (value) {
 exports.createServer = function () {
   var args = Array.prototype.slice.call(arguments), 
       callback = typeof args[0] === 'function' && args.shift(),
-      options = {}, port, host, forward, silent, proxy, server;
+      options = {}, port, host, forward, silent, proxy, server, handler;
   
   if (args.length >= 2) {
     port = args[0];