py3: byteify gendoc.py This is mostly b'' prefixing, with some cargoculting of help.py to get around `textwrap.dedent()` and __doc__ string requirements.

py3: use bytes stdout in hghave.py This fixes a failure in test-run-tests.t around notarealhghavefeature. It seems crazy to me that all of this needs to be adjusted in all of these tests, but the line as run-tests.py sees it in _processoutput() before doing anything is already mangled with a trailing '\r'. Switching to normalizenewlines=True for TTest works, but I'm sure that breaks other stuff.