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.