[cairo] PDF Backend for cairo

[spitzak at d2.com]

> I've attached the equivalent pdf version.  In acroread, the corner looks
>  perfectly round, but gpdf renders it with artifacts similar to what you
>  describe.  I couldn't get ggv to load it, so I suspect I got an offset
> wrong or something.  Anyway, I'll revisit this later, for now I'm still
> trying to get a feel for how the cairo features map to PDF.

Output looks correct in OS/X's "Preview" program, which I think is using
OS/X's intenal pdf interpreter.