We don't really use `sudo` anywhere, except for installing packages;
this means we should be able to use the faster container-based
environment on Travis, instead of the VM-based one.
This isn't quite as good as I'd like -- the XVFB setup doesn't support
a bunch of context creation extensions that we use, and I haven't
looked into the multiplatform stuff for doing OS X testing yet. I
think it's a good start, though.
Emmanuele Bassi
Eric Anholt