When posting an object via $xhr

$xhr('/some/uri', 'POST', {some:'object'});

The default behavior is to encode that object as JSON. This would be fine if the default Content-Type of $browser.xhr was application/json, but it's application/x-www-form-urlencoded.

Since you can't set the Content-Type via $xhr (see #180), then this feature is virtually unusable, confusing and probably an inappropriate default.

Solution is to urlencode the object instead of JSON