fd leak in ReadStream.destroy()

defensive programming is bad sometimes :)

this leaks:

```js
setInterval(function() {
  var x = require('fs').createReadStream('/etc/passwd');
  x.destroy();
}, 1000);
```

this doesn't:

```js
setInterval(function() {
  var x = require('fs').createReadStream('/etc/passwd');
  x.close();
}, 1000);
```

all details are here somewhere: https://github.com/visionmedia/send/issues/55

I wonder how do I write tests for those...