[Cairo] Color transforms

[Carl Worth]

On Jul 16, Keith Packard wrote:
 > > But what's the best way to fix PostScript? 
 > 
 > My plan was to have cairo emit trapezoids instead of higher-level 
 > primitives.  This will avoid the bugs in PostScript and provide figures 
 > which exactly match the screen.  The alternative would be to accept some 
 > device-dependent variation in the results, and I'm not willing to live 
 > with that.

One other alternative is to characterize the bugs well and use
higher-level primitives in those cases where we trust the PostScript
implementation to draw things correctly.

-Carl