Memory leak caused by setInterval

It seems hardly to resolve this problem in normal way, but [node-sleep](https://github.com/ErikDubbelboer/node-sleep) + `child_process` may be an alternative solution.

``` javascript
// timer.js
var sleep = require('sleep').sleep;
while (1) {
  sleep(1);
  process.send('tick');
}

// reader.js
this.timer = child_process.fork('./timer');
this.timer.on('message', function (msg) {
  // poll
});
```
