MacGui: workaround for a bug in [[NSApplication sharedApplication] applicationIconImage] that happens with 1024x1024 icns on Snow Leopard, the icon in the dock was displayed a bit small.

git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@6459 b64f7644-9d1e-0410-96f1-a4d463321fa5