Issue #22127: Bypass IDNA for pure-ASCII host names (in particular for numeric IPs).
Issue #22127: Bypass IDNA for pure-ASCII host names (in particular for numeric IPs).
Issue #22127: fix typo.
- Issue #21539: Add a *exists_ok* argument to `Pathlib.mkdir()` to mimic
  `mkdir -p` and `os.makedirs()` functionality.  When true, ignore
  FileExistsErrors.  Patch by Berker Peksag.

(With minor cleanups, additional tests, doc tweaks, etc. by Barry)

Also:

* Remove some unused imports in test_pathlib.py reported by pyflakes.
Issue #21972: Make it clear that the PEP 401 future import works,
despite the PEP being rejected.