A command like `mkdir -p nonexistent/.' would create the

A command like `mkdir -p nonexistent/.' would create the
directory but exit nonzero with a diagnostic.  This could also be
triggered with a non-`.' component, e.g., in a race with another
process running the same `mkdir -p nonexistent/sub' command.

(make_dir_parents): Handle the case of an existing final component.
Reported by Matthias Andree here:
http://savannah.gnu.org/bugs/?func=detailitem&item_id=14848