add logind sleep ability

With upower 0.9.20, sleep and hybernate functions of upower
declared deprecated. All applications should use logind for
sleep/hybernate. So, there is an implementation of
logind-powered sleep for mpm.
crash when suspending via logind fixed

On some machins it seems to be a race condition in dbus
when suspend via systemd. Here is a workaround.
Merge pull request #55 from boyarsh/master

Add ability to suspend/hibernate via logind