Features:
+* maybe add "systemctl edit" that copies unit files from /usr/lib/systemd/system to /etc/systemd/system and invokes vim on them
+
* dbus: add new message hdr field for allowing interactive auth, write spec for it. update dbus spec to mandate that unknown flags *must* be ignored...
* maybe introduce AssertXYZ= similar to ConditionXYZ= that causes a unit to fail (instead of skipping it) if some condition is not true...