[cairo] Blend modes take 3

[Adrian Johnson]

Benjamin Otte wrote:
> Hey,
> 
> After Emmanuel's [1] and my [2] previous attempt, I've started the
> third attempt to get SVG and Flash blend modes into Cairo. And this
> time I'm dead serious. I intend to merge my current work once 1.9
> opens unless there's any objections.
> I've published git repositories containing my work [3]. I regularly
> rebase them on top of current master. The code is complete, I just
> need to cleanup the commit order at some point.

And here is an implementation of the additional blend modes for PDF.

   http://cgit.freedesktop.org/~ajohnson/cairo/log/?h=blend-mode-pdf

I have not done much testing of this. However it is sufficient to run 
the extended-blend test and view the PDF output in acroread or poppler 
with the Splash backend. As the cairo backend of poppler does not 
currently support these blend modes, viewing the 
extended-blend-pdf-*-out.png files will not be interesting.