[XHR] Handle All Status Codes

I'm sure 1000 people have said this before me, but here it is again to 
show we really want this feature.

I think the XMLHttpRequest object should handle all status codes during 
a GET, POST or PUT requests.  More specifically, redirects codes (30x) 
should be set and the "onreadystatechange" event should be fired.  I 
don't see any problem with transparent redirects, not everyone cares if 
a request gets redirected.  However, if someone checks the status code 
during the onreadystatechange event and it returns a 30x value they 
should be able to abort the request.