py3: fix bad escapes of sub() replacement pattern in test-template-basic.t Python 3.7 starts complaining about it. We have to double the backslash or '\x5c' to get around.

perfdiscovery: benching findcommonheads() This works between the local repo and any peer given by its path, and should be useful for further work on discovery Differential Revision: https://phab.mercurial-scm.org/D5418

windows: ensure pure posixfile fd doesn't escape by entering context manager There are tests in test-revlog-mmapindex.t and test-rebase-mq-skip.t that are fixed by this, but we usually don't use --pure on Windows. For whatever reason, the remaining --pure failures are various errors like $ENOTDIR$ and "Access is denied" have a trailing '.'.

vfs: ensure closewrapbase fh doesn't escape by entering context manager I'm not sure if there's a problem in practice here, as there's no test failure either way. The __exit__() and close() methods raise an exception, so maybe __exit__() and close() are being called directly on the underlying handle when delayclosedfile is used on a context manager? I doubt that was intended.