Symbolic names for table entries in conditionals, closes #928376:

(ef_elt_byname): New.
(nstr_match_val): Use it to generalize to arbitrary table with
uniquely named elements.  Use ca_type to find table, remove parameter
type.  Callers changed.
(nstr_mkselval): Adapt sanity check accordingly.
(NSC_TYPEID): No longer needed, remove, users changed to use
appropriate integer type instead.  This fixes signedness of sector
selectors des and newdes.
(meta_type): Remove entry for NSC_TYPEID.
(nstr_coerce_val): Can't detect typeid - integer mismatch anymore.
Was nice to have; perhaps revive it later.

src/lib/global/symbol.c

@@ -86,7 +86,6 @@ struct symbol meta_type[]  = {
     {NSC_LONG, "d"},
     {NSC_DOUBLE, "g"},
     {NSC_STRING, "s"},
-    {NSC_TYPEID, "d"},
     {NSC_CHAR, "d"},
     {NSC_UCHAR, "d"},
     {NSC_SHORT, "d"},