[Cairo] Color transforms

[Keith Packard]

Around 20 o'clock on Jul 16, David Forster 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.

-keith