We can only apply a configuration if its outputs match the connected
ones, so discard the current configuration if the set of output changes
(for example for hotplug), otherwise we will crash trying to apply
the bogus previous configuration.
https://bugzilla.gnome.org/show_bug.cgi?id=725637
Apparently some connector technologies don't distinguish between
on and off, and there might be valid use cases for running without
any connected monitor.
In that case, just avoid any configuration at all.
https://bugzilla.gnome.org/show_bug.cgi?id=709009
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.
