images / alpha-blending

[David Reitter]

I am trying to use a few new icons for the tool-bar and after a bit  
of fruitless research, I have the impression that alpha-blending is  
not supported. I can only use bitmasks, even with image types such as  
PNG that have an alpha channel. Is that correct?

(I have only tried this with the Carbon port, but I understand that  
X11 currently doesn't support alpha-blending anyways.)