Message 277797 - Python tracker

Thanks for the patch, masamoto, and thanks for the review and rebase, erik.bray!

I only applied this to 3.7.  It's much more open to experimentation currently, and we have a way to go before Python can even be built on Cygwin.  Once we reach a more stable point (say, the full test suite can be run, even if not everything passes), we can evaluate whether backporting all the changes it took to get there is worthwhile.