Issue #19456: ntpath.join() now joins relative paths correctly when a drive
is present.
Idlelib: forward port changes that silenced 2.7 -3 deprecation warnings and
which are at least as efficient. On Py3, unpacking exceptions never works.
Issue #20424: Python implementation of io.StringIO now supports lone surrogates.
Issue #20373: generalize use of test.script_helper in test_warnings.  Patch by Arfrever.
inspect.docs: Document constructors for Signature & Parameter #20442
Remove issue 19081 Misc/NEWS entry since it isn't entirely fixed yet.