Use of Color++ mode.
8/8/04 dhb Started it.
18/4/05 ejw Converted it to run with OSX version of Psychtoolbox
10/24/13 dhb Pass scaling args to packing routine and truncate test image.
These were needed to make this work with my Bits++ in Color++ mode
today. I think the cropping has to do with the spatial res of my
monitor. How this ever worked without the scaling args, though,
is unclear to me.