(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.
other. Ensure headers in include/ can be included in any order
(except for econfig-spec.h, which is special). New header types.h to
help avoid inclusion cycles. Sort include directives. Remove some
superflous includes.
thread entrypoints:
(lwpSelect, shutdown_sequence): Parameters didn't match thread entry
point prototype.
(lwpEntryPoint): Arguments didn't match thread entry point prototype.
Change linkage of functions without prototype declaration to static
where possible.
Remove some superflous declarations, replace others by suitable
includes.
