fix statusCode != 200 for put and delete + passing http response to the cb

* added http error handling for put and delete.
* let the client handle the http response
* looks like the client was using readStream instead of keyStream, now calling /keys on the server (right?)
well actually i use it only to check the statusCode of the request to see if the request failed for 404. I'm mounting the multilevel-http express app to a base path like this:

```javascript
app.use('/bucket/people',multilevel.server('/data/people'))
```

the request may fail because either the "mount" does not exists (404) or because the key is not found by level db. Generally, because someone could use multilevel-http in his express app, it might be usefull to retrieve the (eventually custom) response.