Added onprogress callback when doing XDR

The absence of onprogress XDR callback causes intermittent aborted requests on IE 9 due to a bug in that browser.
See http://social.msdn.microsoft.com/Forums/ie/en-US/30ef3add-767c-4436-b8a9-f1ca19b4812e/ie9-rtm-xdomainrequest-issued-requests-may-abort-if-all-event-handlers-not-specified

Also formatted the source code slightly to make spacing more consistent.