according to context, to make `lstat * ?type#spy&spy>1' work. Closes
bug#825363, #905809, #905814 and #922968.
(nsc_type, packed_nsc_type, nsc_cat, packed_nsc_cat, nsc_flags): New.
(valstr): New. Old code encoded values in type long, which was
somewhat hard to read and could only support signed integer values.
(nscstr): Redesign. Use valstr. Typed operator.
(castr): Split ca_code into ca_type, ca_flags, ca_off. Tables
changed.
(nstr_comp, nstr_exec): Redesign and rewrite. Callers changed. They
used the old design incorrectly, which let players smash the stack
by supplying more than NCOND conditions.
(encode, nstr_comp_val, decode, nstr_exec_val): Rename, redesign, and
rewrite. Callers changed.
(nstr_coerce_val): New.
(var_ca, sect_ca, ship_ca, land_ca): Checking both var_ca[] and the
object's ca complicates proper recognition of unique abbreviations.
Copy contents of var_ca[] into the ca of objects, remove var_ca[].
(surv): Reject values with category other than NSC_OFF and types that
can't be coerced to NSC_LONG. Old code happily passed values with
category NSC_VAL to code_char(). The previous version interpreted
them correctly, but earlier versions interpreted them as NSC_OFF, then
logged `bad type in decode: 0' and evaluated them into zero.
(code_char): Used to test category NSC_VAR to decide whether to
display tens or hundreds. NSC_VAR no longer exists. Test type
instead. Makes more sense anyway.
