as far as i know, _.extend doesn't do a proper deep extend, for example

```javascript
var bar = {
  headers: {
    Blah: 'Blah',
    Accept: 'application/xml'
  }
};
_.extend(bar, { headers: { Accept: 'application/xml' } });
// -> bar = { headers: { Accept: 'application/xml' } }
```

if you can find a workaround then go ahead :)