[poppler] Support for cairo rendering with cpp front end?

[Richard Stephen Uhler]

I recently updated my pdf viewer to use the cpp interface to poppler, and I
see that it uses the splash rendering back end. I think the cairo rendering
back end looks better though, so I've hacked up a version of cpp page
rendering which use cairo instead of splash. The patch I've been using is
attached.

Do you have any interest in this patch? Is there some way I can help to get
this included in poppler? I didn't work very hard to figure out the right
way to update the makefiles or support cairo and splash at the same time or
test the changes. If you have recommendations for how to do that better and it
would help, I would be happy to clean up the patch.

    Thanks,
    Richard