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.