(_D_EXACT_NAMELEN): Renamed from NLENGTH, for

(_D_EXACT_NAMELEN): Renamed from NLENGTH, for
convenience on GNU systems.  All uses changed.  Don't bother
looking for any dirent.h substitute other than ndir.h.
(D_INO): Remove unnecessary parentheses.
(IN_CTYPE_DOMAIN, ISGRAPH, ISPRINT, ISALNUM, ISALPHA):
(ISCNTRL, ISLOWER, ISPUNCT, ISSPACE, ISUPPER, ISXDIGIT):
(ISDIGIT_LOCALE, TOLOWER, TOUPPER): Remove.  All uses changed
to ctype.h equivalents.
(isblank): Renamed from ISBLANK.  Check for HAVE_DECL_ISBLANK too.
All uses changed.