procutil: make stdout line-buffered on Windows if connected to TTY
Windows doesn’t support line buffering. Previously, we worked around that by
setting the stream unbuffered. Instead, we can use our own line buffering we
already use on Python 3.
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https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
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If you can't run the entire testsuite for some reason (it can be
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273ce12ad8f1` will report some style violations on a very old commit).