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
struct lndstr members lnd_spy, lnd_rad, lnd_ammo, lnd_fuelc,
lnd_fuelu, lnd_maxlight, lnd_maxlight are mere copies of struct
lchrstr members l_spy, l_rad, l_ammo, l_fuelc, l_fuelu, l_nxlight,
l_nland. Remove them.
Make land unit selectors spy, rmax, ammo, fuelc, fuelu, maxlight
virtual.
New pln_att(), pln_def(), pln_acc(), pln_range_max(), pln_load()
replace the struct plnstr members with the same names.
Make plane selectors att and def virtual.
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.
