By default the middle button is in a compatibility mode, and generates
standard wheel events when dragging with the middle trackpoint button.
Unfortunately this is buggy:
* The middle button comes up before starting wheel events, causing a middle
  click on whatever the mouse cursor was sitting on
* The USB keyboard always generates the "native" horizontal wheel event,
  regardless of mode.

Instead, enable the "native" mode the Windows driver uses, and add support
for the custom events this generates. This fixes the USB keyboard wheel
events, and the middle-click up event comes after the wheel events.

Signed-off-by: Jamie Lentin <jm@lentin.co.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>