Features:
+* logind: maybe watch utmp asynchronously using inotify, and populate our own
+ tracked session metadata from the fields available therein. Why bother? Right
+ now, all "ssh" sessions will be tracked without their TTY by logind (which is
+ not just unfriendly to users as this means "loginctl session-status" shows
+ less information than "who" in many cases, but also breaks the IdleAction
+ logic, as we never can detect such sessions as idle, as we have no TTY to
+ watch). ssh sets the PAM_TTY field on its PAM sessions to "ssh" rather than
+ the actual pty, because the PAM session is opened early on for new
+ connections, but the PTY only registered much later (if at all). ssh writes
+ the utmp record only after a TTY is actually registered, hence we could use
+ this data then, and use it if it is available. Using utmp for this is ugly of
+ course, and watching things asynchronously even more so, but it should be
+ good enough for the idle detection logic at least.
+
* Add a "systemctl list-units --by-slice" mode or so, which rearranges the
output of "systemctl list-units" slightly by showing the tree structure of
the slices, and the units attached to them.