(mouse-wheel-change-button): Deactivate before changing.

(mouse-wheel-change-button): Deactivate before changing.
(mouse-wheel-up-button, mouse-wheel-down-button): Obsolete.
(mouse-wheel-up-event, mouse-wheel-down-event): New vars.
(mouse-wheel-follow-mouse): Change default to t.
(mwheel-event-button): Return the basic event symbol.
(mwheel-scroll): Work with non-mouse events.
(mouse-wheel-mode): Use the new vars.
(mwheel-install): Obey `uninstall'.