Fix compizconfig building protobuf more

That sentence sucks, but that's ok, because the build sucks too. Still not
working as it should. The good thing is that there's nothing at all
reporting anything wrong, it just doesn't work. So that's something.
Add some verbosity to image loading

This alleviates a bit of #3 , but isn't a good solution.

The fundamental problem is listed in #27 :

Image plugins are wacko, and the "try every combination of paths and
suffixes we can imagine" thing is making it much more complex than it
should be to report why we can't open an image.