[racket-dev] Windows horizontal mouse wheel

The `racket/gui' library now supports horizontal mouse-wheel events,
but I don't have a Windows machine with a mouse that support horizontal
wheel events. As likely as not, I've implemented it backwards for Win32
(i.e., it's tricky atbest to match positive/negative with left/right
based on the docs).

Can someone who does have such a Windows mouse run

 racket -l tests/gracket/showkey

with the latest and tell me whether horizontal wheel events are correct
or backwards?

Thanks,
Matthew