(make_dir): Remove. All uses replaced by mkdir.

(make_dir): Remove.  All uses replaced by mkdir.
(make_dir_parents): Last arg is now int * (for errno), not bool *.
Rewrite "mkdir -p" algorithm to avoid the need for "stat"
each time through the loop.  Do not diagnose restore_cwd failure;
that is the caller's job (and perhaps the caller does not care).