Merge branch 'kb/checkout-optim'

* kb/checkout-optim:
  Revert "lstat_cache(): print a warning if doing ping-pong between cache types"
  checkout bugfix: use stat.mtime instead of stat.ctime in two places
  Makefile: Set compiler switch for USE_NSEC
  Create USE_ST_TIMESPEC and turn it on for Darwin
  Not all systems use st_[cm]tim field for ns resolution file timestamp
  Record ns-timestamps if possible, but do not use it without USE_NSEC
  write_index(): update index_state->timestamp after flushing to disk
  verify_uptodate(): add ce_uptodate(ce) test
  make USE_NSEC work as expected
  fix compile error when USE_NSEC is defined
  check_updates(): effective removal of cache entries marked CE_REMOVE
  lstat_cache(): print a warning if doing ping-pong between cache types
  show_patch_diff(): remove a call to fstat()
  write_entry(): use fstat() instead of lstat() when file is open
  write_entry(): cleanup of some duplicated code
  create_directories(): remove some memcpy() and strchr() calls
  unlink_entry(): introduce schedule_dir_for_removal()
  lstat_cache(): swap func(length, string) into func(string, length)
  lstat_cache(): generalise longest_match_lstat_cache()
  lstat_cache(): small cleanup and optimisation

combine-diff.c

@@ -712,9 +712,7 @@ static void show_patch_diff(struct combine_diff_path *elem, int num_parent,
 			result_size = buf.len;
 			result = strbuf_detach(&buf, NULL);
 			elem->mode = canon_mode(st.st_mode);
-		}
-		else if (0 <= (fd = open(elem->path, O_RDONLY)) &&
-			 !fstat(fd, &st)) {
+		} else if (0 <= (fd = open(elem->path, O_RDONLY))) {
 			size_t len = xsize_t(st.st_size);
 			ssize_t done;
 			int is_file, i;