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.
