* properly handle .mount unit state tracking when two mount points are stacked one on top of another on the exact same mount point.
Features:
+
+* expose switch-root in systemctl
+
+* remove old root in switch-root logic
+
* improve !/proc/*/loginuid situation: make /proc/*/loginuid less dependent on CONFIG_AUDIT,
or use the users cgroup information when /proc/*/loginuid is not available.