This backports the fix from #16611, per discussion with the release
manager.

These added a path attribute to pathlib.Path objects, and docs.
Instead, we're going to use PEP 519.

(Starting in the 3.4 branch and merging forward from there since that's what I did originally.)

On Windows a symlink can has the FILE_ATTRIBUTE_DIRECTORY flag.

Patch by Liang-Bo Wang.

Patch from Chi Hsuan Yen.

"certificate verify failed " and "CERTIFICATE_VERIFY_FAILED " as
some SSL libraries use different text than OpenSSL.