(set, mission, multifire, fuel, cons_choose, cede): Use it instead of
ef_byname(). Remove the hacks to map unwanted results to wanted
results. The hacks in set() were broken: bad input made the code cast
arbitrary items to union trdgenstr, with potentially disastrous
consequences. Closes#906483 and #906486.
(set): Less cryptic prompt and diagnostics.
freshly extended trade file makes sense. When set() removes a lot,
simply zero the slot.
(set): Initialize trd_uid.
(trade_check_ok): Use check_land_ok() & friends instead of doing it by
hand, but wrong. This fixes bying planes and land units loaded on
ships that moved after loading.
(check_trade_ok): New.
(trade_check_ok): Use it. Remove unused argument lot. Callers
changed.
To save space, the ancients invented `variables': a collection of
key-value pairs, missing means zero value, space for `enough' keys.
This complicates the code, as assigning to a `variable' can fail for
lack of space. Over time, `enough' increased, and for quite some time
now `variables' have been *wasting* space. This changeset replaces
them, except in struct mchrstr, struct lchrstr and struct pchrstr,
where they are read-only, and will be replaced later. It is only a
first step; further cleanup is required. To simplify and minimize
this necessarily huge changeset, the new item[] arrays have an unused
slot 0, and the old variable types V_CIVIL, ... are still defined, but
must have the same values as the item types I_CIVIL, ...
(genitem_ca, ship_ca, plane_ca, land_ca): Remove selector "sell".
(comstr, trdstr): Members trd_price, com_price have no effect. Use
them instead of trd_maxprice, com_maxprice and remove the latter.
(commodity_ca, trade_ca): Remove selector "maxprice".
