Prevent auto-redirect on 30x response in node

I have a use-case where I do not want to auto redirect upon a 30x,
because I need to adjust the outgoing headers for the subsequent request.

I fear this issue's fate will be similar to #64, since xhr2's source code is pretty
clear about it's semantics: https://github.com/pwnall/node-xhr2/blob/567ec5f41f94f0bcb6d6b1f917be6506f43ce49a/src/001-xml_http_request.coffee#L501-L519