So, here's a patch with a reimplementation of QZ_SetIcon() that does what I
described above. I apologize for the delay, I've been quite busy in the last
few days.

It appears to work here on 10.4.5 PPC in the limited testing that I've done;
I'll try to test it on 10.3.9 and 10.2.8 as well, but that might take another
week or so. Please test on i386.

Regarding alpha channels, per-surface alpha, and color keys, the same semantics
as for regular blits to an RGB surface should apply (for the final icon
composited onto the dock), unless I made a mistake - except in one pathological
case: if the icon surface has an alpha channel, its SDL_SRCALPHA flag is not
set (i.e. it has been explicitly cleared, since it's on by default for RGBA
surfaces), and it has a color key, plus an explicit mask was specified (instead
of the one autogenerated from the colorkey), then the color-keyed areas appear
black instead of transparent. I found no elegant way of fixing this, was too
lazy to implement the inelegant one, and decided that it isn't worth the effort
(but if someone disagrees, I can do it).

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401773