systemd detection. Tested on CentOS 6 (Red Hat init) and 7 (systemd),
Devuan (Debian init), and Debian 9 (systemd).
Add RCDBOOT_STYLE to BUILD_DEFS.
Bump version.
dependency ordering, so we compute the order of such rc.d scripts as are
present at install time (via a new "list" action in sbin/rc.d-boot).
Anything added or removed later is the sysadmin's job. I guess this is
what OpenBSD sysadmins expect.
While here, make "stop" run the commands in reverse order, like NetBSD
does on shutdown.
Bump version.
