core: fix double free
systemctl: rework is-active and is-failed code
systemctl: don't hit an assert if we try to reboot and dbus is dead

https://bugzilla.redhat.com/show_bug.cgi?id=889624
systemctl: honour inhibitors only when running unprivileged
core: add bus API and systemctl commands for altering cgroup parameters during runtime
bootchart: no need for memset here
systemctl: numerous modernizations
systemctl: be smarter when mangling snapshot names

For "systemctl snapshot" it makes no sense to complete an incomplete
name with ".service" as we previously did, use ".snapshot" instead.
Also, don't bother with mount units or suchlike, we know that this must
be a snapshot and hence is the only sane way for completion.
update TODO
systemctl: drop compat with really really old systemd versions