[cairo] Optimize spans in the trapezoid rasterizer

[Billy Biggs]

> Carl Worth (cworth at cworth.org):
> 
> > But, the patch doesn't seem to give correct results for me. Here's
> > what I see for the fill-rule test for example:
> > 
> > http://cairographics.org/~cworth/images/fill-rule-image-out-broken.png
> > 
> > (Where the star shapes are intended to be filled, of course.)

  For the benefit of the list, the problem was my using of the inline
attributes with Carl's version of gcc (4.0.0 from Red Hat).

  -Billy