Add a trace when a empty response is send

lib/http.js

@@ -591,6 +591,7 @@ OutgoingMessage.prototype.write = function(chunk, encoding) {
   }
 
   if (!this._hasBody) {
+    console.trace();
     console.error('This type of response MUST NOT have a body. ' +
                   'Ignoring write() calls.');
     return true;