It seems that the changes to X input exposed a problem that wasn't detected
before. The axis clipping code in GetPointerEvents() uses those limits to
constrain the pointer's coordinate range. The max was zero so the pointer
couldn't move.
Use new dmxCoreMotion2() function which enqueues motion events with
GetPointerEvents()/mieqEnqueue().
The clipAxis() code in GetPointerEvents() is causing some grief. The
limits seem to have always been (0,0) according to the original calls
to InitValuatorAxisStruct() in dmxinputinit.c.
Terrible hack for now: Call InitValuatorAxisStruct() with hard-coded max
values of 1280 (my screen width).
