fsmonitor: fix str/bytes mismatch when accessing watchman version There were 2 bugs here. First, keys in the tuple are always str. Second, we needed to normalize the value to bytes to prevent a str/bytes mismatch on Python 3. With this commit, `hg debuginstall` with fsmonitor enabled now works on Python 3. Differential Revision: https://phab.mercurial-scm.org/D7205