BitsPlusBlank(screen)
Just zero the Bits++ clut to save the screen.
Probably shouldn't be called when screen is open.
5/4/03 dhb Wrote it.
9/20/03 dhb Needs screen pointer.
18/4/05 ejw Converted it to run with OSX version of Psychtoolbox
Psychtoolbox/PsychHardware/BitsPlusToolbox/BitsPlusBlank.m