Testsuite and Python 3

Hello everyone, Note that yesterday I flipped the switch in the build system to use the Python 3 interpreter by default when invoking the testsuite driver. The motivation for this is the fact that Python 2.7 is quite buggy on Windows, which resulted in spurious testsuite failures (see #12554). The question remains, however, of how much we care to preserve compatibility with Python 2. From what little I've seen so far I think it would be easier for everyone involved if we just let Python 2 pass into the sunset. Afterall, Python 3 is no less available than 2 at this point. Thoughts? Cheers, - Ben