[NEW] devel/py3-pytest-xdist: Create Python 3.x version of port
The latest www/py-requests update  unbundled its dependencies, now
requiring chardet, idna, urllib3 and certifi from ports.
www/py3-requests port was not tested during QA, which would have highlighted
the need for many new py3-* ports (and their dependencies).
This change creates one of those ports.