The code in MetaMonitorConfig was really complex and was trying to do
way too much, using multiple different variables to determine where
things were stored, and trying to do fancy tricks to transfer
ownership.
Add a refcounting system to help simplify this, and clean up the logic.
Simply along the way, this fixes multiple bugs in the monitor config
logic, most notably bug #734889, which was my original goal to fix.
meta_monitor_config_match_current() only matches the number of outputs
and if the output connector, vendor, product and serial match.
In the X backend, this means that we can't use it to bypass doing any
work because it won't detect cases where we actually want to update
ourselves like e.g. an output being turned off either by us or by
another X client (e.g. xrandr).
In the native backend, unlike the xrandr backend, we only get called
on real hotplug events and thus should always trigger the common
hotplug code to (possibly) apply a new mode so the check is pointless
anyway.
https://bugzilla.gnome.org/show_bug.cgi?id=738630
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.
