SET_SAFE_LOGOUT_ACTION:  Tell the daemon to halt/reboot/suspend
after everybody logs out.  If only
one person logs out, then this is
obviously the same as the
SET_LOGOUT_ACTION.  Note that
SET_LOGOUT_ACTION has precedence over
SET_SAFE_LOGOUT_ACTION if it is set to
something other then NONE.  If no one
is logged in, then the action takes
effect immediately.
Only supported on connections that passed AUTH_LOCAL.
Supported since: 2.5.90.0
Arguments:  <action>
NONE           Set exit action to 'none'
HALT           Set exit action to 'halt'
REBOOT         Set exit action to 'reboot'
SUSPEND        Set exit action to 'suspend'
Answers:
OK
ERROR <err number> <english error description>
0 = Not implemented
7 = Unknown logout action, or not available
100 = Not authenticated
200 = Too many messages
999 = Unknown error
