Log message

implements white on mask (and added black on mask) in copy_mono.

This adds white on mask as mask=black and (D & ~S) | S .
Black on mask is treated specially as (S & D). Fixes bug 688372
(which uses white on mask) and 690830 (which uses black on mask)
and 690025 (which uses both white on mask and black on mask).

	Modify	/trunk/gs/base/gdevpx.c	diff