+ fts: add/use new struct member, fts_dirp
+ We are about to use this to manage any directory with
+ too many entries to read all of them into memory at once.
+ To do that, we'll need to save the DIR* pointer in each
+ affected FTSENT struct.
+ * lib/fts_.h: Include <dirent.h>.
+ (struct FTSENT) [fts_dirp]: New member.
+ * lib/fts.c (closedir_and_clear): Define.
+ Use it in place of closedir so that we are sure to
+ clear the new fts_dirp member when done with it.
+ (fts_alloc): Initialize the new member.
+ (fts_lfree): Free, if needed.
+