randr: Use XRRGetScreenResourcesCurrent (rhbz#888821)

randr: Use XRRGetScreenResourcesCurrent (rhbz#888821)

Using XRRGetScreenResources, causes the X-server to actively check for
new monitors, which generates Xrandr events even if nothing is changed, which
causes gnome-setting-manager to muck with the settings, racing with the
agent doing the same.

XRRGetScreenResourcesCurrent OTOH simply returns the last known settings
without any polling of the hardware and matching events being involved.

So use XRRGetScreenResourcesCurrent instead of XRRGetScreenResources, with
one exception. When the number of monitors is changed, so some outputs are
enabled or disabled, then the hardware polling is necessary to properly
reflect the connected / disconnected state in xrandr.

This requires Xrandr >= 1.3, note that since 0.12.0 we already depended
on >= 1.2 anyways, this patch raises the requirement to 1.3 and makes
it explict.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>