client _handleResponse: allow string form of peer.ip

[BEP-3](http://bittorrent.org/beps/bep_0003.html) states:
> peers maps to a list of dictionaries corresponding to peers, each of which contains the keys peer id, ip, and port, which map to the peer's self-selected ID, **IP address or dns name as a string**, and port number, respectively.

The [Theory.org Wiki](https://wiki.theory.org/BitTorrentSpecification#Tracker_Response) agrees.

Is there any evidence of binary ip fields in the wild? Anyway, this code should support both.