The old code didn't honor command abortion at the following prompts:
* arm third argument
* deliver fourth argument (also simplify)
* fire third argument
* fly and recon prompt for carrier to land on: pln_onewaymission()
treated abort like empty input, which made planes attempt landing in
the sector.
* lmine second argument
* order d fourth argument
* power c nat(s) argument
* range second argument
* sail second argument
* shutdown both arguments (first one was broken in commit 84cfd670,
v4.3.10, second one never worked).
* tend third argument
(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.
