Bug: client doesn't return error for bad http codes

Example: if the server responds with `Internal Error 500`, the params returned by the `request` module are `(null, res, body)` [and res.statusCode === 500].

We need a 'middleware' kind of function that checks for the `statusCode`, otherwise the client may be tricked into believing `db.del` || `db.put` (and others) succeeded.

I'll work on this.