The last set of check-ins that introduces Image I/O API use in the
Carbon port (22 branch) broke PNG display; my PNGs are all blue-on-
white now (both in tool-bar and when loaded in a buffer).
I didn't specifically set USE_MAC_IMAGE_IO, so it is at its default
(FALSE or not defined unless I'm mistaken).
I can make one of the PNGs available and investigate further if that's
required.