Requiring systemd for the gnome-settings-daemon power plugin

[Bastien Nocera <hadess hadess net>]

Hello,

I intend on making systemd a hard requirement for the power plugin in
gnome-settings-daemon. There is a lot of interactions and external
factors involved in making policy decision about power. This makes the
power plugin one of the more fragile parts of the system, with things
like DPMS, screensaver activation, screen locking, brightness control,
suspend policy, battery information exporting, all handled in the same
codebase.

Using systemd to request suspends means that:
- things work out of the box when people do not use GNOME (no need to
install acpid which then conflicts with GNOME)
- inhibitions are per-system instead of per-user
- application get more information about suspending
- simplify the power plugin's codebase a great deal

The patches I will commit are here:
https://bugzilla.gnome.org/show_bug.cgi?id=680689

Additionally, and separately, support for ConsoleKit usage for
session-tracking will be removed.

Cheers