Buffer implementation for makedrive

I hate these deep loops.  Why not change it to something like this? (NOTE: I haven't tested this)

```javascript
function processDiff(diff) {
  if(diff.contents) {
    diff.contents.forEach(processDiff);
  } else {
    if(Buffer.isBuffer(diff.data)) {
      diff.data = diff.data.toJSON();
    }
  }
}

diffs.forEach(processDiff);
```