fsmonitor: refresh pywatchman to upstream
Update to upstream to version c77452. The refresh includes fixes to improve
windows compatibility.
There is a minor update to 'test-check-py3-compat.t' as c77452 no longer have
the py3 compatibility issues the previous version had.
# no-check-commit
#
# Avoid interference from actual test env:
unset HGTEST_JOBS
unset HGTEST_TIMEOUT
unset HGTEST_PORT
unset HGTEST_SHELL