[cairo] Use 8-bit colour values internally

[Bill Spitzak]

You can also do ((c) * 0x101) which I believe is just as fast or faster 
than the shift+add on modern machines.

MenTaLguY wrote:
> On Mon, 2005-08-22 at 23:37 -0400, Jason Dorje Short wrote:
> 
> 
>>#define COLOR_INT_TO_SHORT(c) ((c) << 8)
> 
> 
> If you're going to do that, it may as well be:
> 
> #define COLOR_INT_TO_SHORT(c) (((c) << 8) | (c))
> 
> which is (macro side-effects aside) equivalent to the correct: 
> 
> #define COLOR_INT_TO_SHORT(c) ((c) * 65535 / 255)
> 
> Which yields the expected 65535 for COLOR_INT_TO_SHORT(255), instead of
> 65280.