Abstract from shutdown initiation mechanism:

Abstract from shutdown initiation mechanism:
(shutdown_initiate): New.
(shut): Use it.  Shutdown in zero minutes no longer cancels the
shutdown, it just works.  Use negative argument to cancel.  Logging is
less detailed.
(shutdown_sequence): Internal linkage.

(pr_wall): All callers prefix text it with the same header.  Move it
into the function.