payload fixes and XDomainRequest workaround

- don't serialize FormData payloads
- fix query string when url already have '?'
- fix requests from IE8/IE9 using XDomainRequest (must define `onprogress`/`ontimeout` callbacks)

It seems that Internet Explorer needs workarounds using onprogress/ontmeout and setTmeout(func, 0) for `send()`. Kinda weirdness: http://stackoverflow.com/questions/15786966/xdomainrequest-aborts-post-on-ie-9