Sectors need space for items, deliveries and distribution thresholds.

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, ...

src/lib/global/item.c

@@ -59,3 +59,5 @@ struct ichrstr ichr[I_MAX + 2] = {
     {'r', V_RAD, 150, 1, 8, {1, 10, 1, 1}, "radioactive materials"},
     {0, 0, 0, 0, 0, {0, 0, 0, 0}, 0}
 };
+
+int itm_maxno = (sizeof(ichr) / sizeof(struct ichrstr)) - 1;