This handles display of the
EyeLink camera images. While in imaging mode, it
continuously requests and displays the current camera image. It also displays
the camera name and threshold setting. Keys on the subject PC keyboard are sent
to the tracker so the experimenter can use it during setup. It will exit when
the tracker leaves imaging mode or disconnects. RETURNS: 0 if OK, 32767 (
Ox7FFF
or TERMINATE_KEY) if pressed, -1 if disconnect