really recreate socketio-client in expressCreateServer, fixes #2342

When using plugins, the express server gets restarted. When we do that,
the socketio-server should also get restarted. It doesn't. That means
that all the events in SocketIORouter.js are bound twice, which causes
chaos all over etherpad.

This changes our socketio.js so it fully recreates the io-instance when
we restart the server.

introduced in 95e7b0f156, but catching
that would have been hard.

src/node/hooks/express/socketio.js

@@ -1,24 +1,22 @@
 var log4js = require('log4js');
 var settings = require('../../utils/Settings');
+var socketio = require('socket.io');
 var socketIORouter = require("../../handler/SocketIORouter");
 var hooks = require("ep_etherpad-lite/static/js/pluginfw/hooks");
 var webaccess = require("ep_etherpad-lite/node/hooks/express/webaccess");
 
-// there shouldn't be a browser that isn't compatible to all 
-// transports in this list at once
-// e.g. XHR is disabled in IE by default, so in IE it should use jsonp-polling
-
-var socketio = require('socket.io')({
-  transports: settings.socketTransportProtocols
-});
-
 var padMessageHandler = require("../../handler/PadMessageHandler");
 
 var connect = require('connect');
  
 exports.expressCreateServer = function (hook_name, args, cb) {
   //init socket.io and redirect all requests to the MessageHandler
-  var io = socketio.listen(args.server);
+  // there shouldn't be a browser that isn't compatible to all
+  // transports in this list at once
+  // e.g. XHR is disabled in IE by default, so in IE it should use jsonp-polling
+  var io = socketio({
+    transports: settings.socketTransportProtocols
+  }).listen(args.server);
 
   /* Require an express session cookie to be present, and load the
    * session. See http://www.danielbaulig.de/socket-ioexpress for more