GnomeRR: refresh the cached view of the screens when mutter restarts

Mutter does a modeset when it starts, but doesn't emit signals,
so we must refresh our structures when we detect that. But most
important, we must ensure that our serial is properly updated,
otherwise any further operation will fail with AccessDenied.

https://bugzilla.gnome.org/show_bug.cgi?id=708284