Issue #19456: ntpath.join() now joins relative paths correctly when a drive
is present.
Refactor the new test for issue19081 to exec import statements into a
test_ns dict instead of the actual globals() and locals().  Suggested
after review by Thomas Wouters.
Remove inaccurate comment and a the related recently added
Py_VerboseFlag print that can never be triggered.

prefix[0] is always equal to 0 at this point in the code.
Remove unneeded use of globals() and locals() in test on imports
introduced with the issue19081 tests.
Idlelib: silence two buildbot Deprecation Warnings with better code.
Silence deprecation warning in sunau.py
Backported a test for lone surrogates support in io.StringIO.
Idlelib & buildbots: suppress py3 deprecation message even if enabled.