xrandr: Prevent possible overflows handling timestamps

The timestamps are gint64 but we cast them down to guint32, which
can cause overflows. Avoid that by passing the timestamps as gint64
all around, even if they are ultimately unused.

https://bugzilla.gnome.org/show_bug.cgi?id=711066
power: Bump the required upower version

As we use the new API.
power: Bump gnome-desktop requirements

For the new API used for the backlight steps.
3.11.1