And use the old "native" backend for both X11 and Wayland. This will
allow us to share fixes between implementations without having to delve
into the XSync X11 extension code.
https://bugzilla.gnome.org/show_bug.cgi?id=705942
Right now this just has all of the files in one directory. We'll
be introducing more structure to this in the future, and build
a proper backend system.