ICNS parsing problems

[Damjan Jovanovic <damjan jov gmail com>]

Hi

I've found 2 bugs in gdk-pixbuf's ICNS parser:
- No support for incremental parsing, which break EoG/Gnome/Nautilus
thumbnailing
- Doesn't skip the first 4 bytes in compressed 128x128 image data,
causing the red color band to be off (or theoretically the entire
image to fail to load)

I've posted a patch for the first issue at
https://bugzilla.gnome.org/show_bug.cgi?id=629474 but it's possible to
also fix this in gdk-pixbuf itself (proposal at
https://bugzilla.gnome.org/show_bug.cgi?id=531059). Can someone please
review/commit it?

Thank you
Damjan Jovanovic