(FTS): New member fts_cycle, that is a union that contains the
old active_dir_ht and cycle_state. All uses changed to mention
fts_cycle.ht and fts_cycle.state.
(FTSENT): New member fts_fts. Remove members fts_ino, fts_dev,
fts_nlink; no longer needed now that fts_statp is always there.
All uses changed to use fts_statp instead.
Include stddef.h, for ptrdiff_t.
(FTS.fts_nitems): Now size_t, not int, for hosts that allow more
than INT_MAX entries in a directory.
(FTS_ROOTPARENTLEVEL): Parenthesize properly.
(FTSENT.fts_level): Now ptrdiff_t, not int, to allow recursing more
than INT_MAX levels deep on 64-bit hosts.
(FTSENT.fts_namelen): Now size_t, not u_short, to support hosts like
the Hurd that don't have arbitrary limits on directory entry lengths.
(FTSENT.fts_statp): Now an array, not a pointer, so that we don't
have to play unportable games with pointer arithmetic. Keep it array
for the benefit of user code that assumes it is a pointer.
(FTS_TIGHT_CYCLE_CHECK): New value.
(FTS_OPTIONMASK): Adjust to include the new value.
(FTS_NAMEONLY, FTS_STOP): Increase to allow room for new value.
(struct FTS) [active_dir_ht]: New member. Replaces fts_dir_signatures.
(struct FTS) [cycle_state]: New member.
encountered in a traversal fit in an `unsigned short',
and fix some portability bugs (don't depend on gcc).
[FTS] (fts_pathlen): Change type from int to size_t.
[FTSENT] (fts_pathlen): Change type from u_short to size_t.
(fts_level): Change type from u_short to int.
