normalised arguments and types for native code

At this point could we check if `error` is a String (if they called `response.fail('an error happened')` for example) and generate the `Error` object for them? It would be a nice convenience so you don't always have to do `response.fail( new Error( 'an error happened' ) );` if all you want to do is send an error message.

```javascript
if ( typeof error === 'string' ) {
  error = new Error( error );
}
```

Would that work?