wireproto: explicitly flush stdio to prevent stalls on Windows This is the key to fixing the hangs on Windows in D2720[1]. I put flushes in a bunch of other places that didn't help, but I suspect that's more a lack of test coverage than anything else. Chasing down stuff like this is pretty painful. I'm wondering if we can put a proxy around sys.stderr (and sys.stdout?) on Windows (only when daemonized?) that will flush on every write (or at least every write with a '\n'). [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2018-March/113352.html

test-lfs: glob over some output changes These changes started with 2090044a288d. They aren't important to LFS testing.

templater: factor out helper that renders named template as string This is quite common in non-web templating, and **kwargs expansion is annoying because of the unicode-ness of Python3.