Removing the 'universal_newlines' and 'encoding' args from the subprocess.check_outputs fuction. 'universal_newlines' is supported in 3.4, but 'encoding' is not. Without specifying 'encoding' it will make a guess at encoding, which can break things on BSD systems. We must handle encoding/decoding ourselves until we can use Python 3.6
Make lint/check-doc.py Python 3.4 compatible.
Also add .python-version for pyenv which will cause tests with too
modern syntax to fail on developer machine rather than on Travis.