http: cork/uncork before flushing pipelined res

Make sure that the pipelined response data will be written as less TCP
packets as possible.

PR-URL: #3172
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

lib/_http_outgoing.js

@@ -161,10 +161,12 @@ OutgoingMessage.prototype._writeRaw = function(data, encoding, callback) {
       var output = this.output;
       var outputEncodings = this.outputEncodings;
       var outputCallbacks = this.outputCallbacks;
+      connection.cork();
       for (var i = 0; i < outputLength; i++) {
         connection.write(output[i], outputEncodings[i],
                          outputCallbacks[i]);
       }
+      connection.uncork();
 
       this.output = [];
       this.outputEncodings = [];
@@ -651,10 +653,12 @@ OutgoingMessage.prototype._flush = function() {
       var output = this.output;
       var outputEncodings = this.outputEncodings;
       var outputCallbacks = this.outputCallbacks;
+      socket.cork();
       for (var i = 0; i < outputLength; i++) {
         ret = socket.write(output[i], outputEncodings[i],
                            outputCallbacks[i]);
       }
+      socket.uncork();
 
       this.output = [];
       this.outputEncodings = [];