[fix] Use workaround for setEncoding bug in node 0.10+ (#527)

The server often crashes with 'TypeError: "list" argument must be an Array of Buffers' errors,
which is caused by a bug in new versions of node, where setEncoding call does not work for messages
that are already in the queue.

This pull request makes sure that concat is never called in the non binary case, even if
setEncoding does not work properly.

lib/transports/polling.js

@@ -154,12 +154,12 @@ Polling.prototype.onDataRequest = function (req, res) {
 
   function onData (data) {
     var contentLength;
-    if (typeof data === 'string') {
-      chunks += data;
-      contentLength = Buffer.byteLength(chunks);
-    } else {
+    if (isBinary) {
       chunks = Buffer.concat([chunks, data]);
       contentLength = chunks.length;
+    } else {
+      chunks += data;
+      contentLength = Buffer.byteLength(chunks);
     }
 
     if (contentLength > self.maxHttpBufferSize) {