fileutils: Make some sample code detect symlinks as intended

The sample code here wasn't a race-free version of the race-susceptible
anti-pattern, because it would have dereferenced a symlink automatically.

Fixes: 293b4923 "Clarify g_file_test() docs about TOCTOU bugs"
Signed-off-by: Simon McVittie <smcv@collabora.com>

glib/gfileutils.c

@@ -329,7 +329,7 @@ g_mkdir_with_parents (const gchar *pathname,
  *    }
  *
  *  // DO THIS INSTEAD
- *  fd = g_open (filename, O_WRONLY);
+ *  fd = g_open (filename, O_WRONLY | O_NOFOLLOW);
  *  if (fd == -1)
  *    {
  *      // check error