#191 skip scroll wheel up event (generates double events)

[David Fries]

Unix has a mouse scroll event button press followed by release
for that button number. For windows just send button press and
skip button release. If the release is sent, it is treated as
a second scroll action on the windows side. Tested with Windows XP.

It's easiest to see when scrolling through a combo box, previously it
would skip entries. Now it doesn't.

[David Fries]

skip mouse wheel up event