py3: use pycompat.bytestr() instead of str()
This is because str() on python 3 return unicodes
setup: sys.version_info always exists
It is documented as existing since Python 2.0, and empirically from
other OSS projects I maintain, there is no problem relying on its
existance.
filelog: fix parsemeta docstring
75bb7c702317 changed the return type of filelog.parsemeta but forgot to
update its docstring.