Fix xhr.responseType set before xhr.open

Not a problem with Chrome, but in Firefox setting it before doesn't work.
See: https://developer.mozilla.org/en-US/docs/Web/API/XMLHttpRequest/HTML_in_XMLHttpRequest#Usage
Emit Node Buffers instead of ArrayBuffers

Browserified [request](http://github.com/mikeal/request) and probably most
Node modules don't handle ArrayBuffers
If encoding is null return Buffer like in Node http
Merged branch bug/behave-more-like-node-http