Find the source of your `sys` deprecation warnings in node@0.6.x

include.js

//
// Place this at the beginning of your node.js program before
// **any and all** require statements.
//
var util = require('util');
var _warning = util._deprecationWarning;

util._deprecationWarning = function () {
  console.trace();
  _warning.apply(util, arguments);
};