Handle two-digit years with leading zeros correctly.

Handle two-digit years with leading zeros correctly.

(textint): New typedef.
(parser_control): Changed from struct parser_control to typedef (for
consistency).  Member year changed from int to textint.  All uses changed.
(YYSTYPE): Removed; replaced by %union with int and textint members.
(tID): Removed; not used.
(tDAY, tDAY_UNIT, tDAYZONE, tHOUR_UNIT, tID, tLOCAL_ZONE, tMERIDIAN,
tMINUTE_UNIT, tMONTH, tMONTH_UNIT tSEC_UNIT, tSNUMBER, tUNUMBER,
tYEAR_UNIT, tZONE, o_merid): Now of type <intval>.
(tSNUMBER, tUNUMBER): Now of type <textintval>.
(date, number, to_year): Use width of number in digits, not its value,
to determine whether it's a 2-digit year, or a 2-digit time.
(yylex): Store number of digits of numeric tokens.
Return '?' for unknown identifiers, rather than (unused) tID.