```
app.use(function *() {
  this.body = 'hello';
});
```

```
 curl -X HEAD http://localhost:7002 -I
HTTP/1.1 200 OK
X-Powered-By: koa
Content-Type: text/plain; charset=utf-8
Content-Length: 5
Date: Tue, 08 Apr 2014 15:52:39 GMT
Connection: keep-alive
```

it still set by `response.body=`, only `status.empty(code)` will remove these headers