[PATCH 1 of 2] py3: add b'' to a few strings in pycompat

[Yuya Nishihara]

On Thu, 13 Sep 2018 19:48:18 -0400, Matt Harbison wrote:
> # HG changeset patch
> # User Matt Harbison <matt_harbison at yahoo.com>
> # Date 1536813542 14400
> #      Thu Sep 13 00:39:02 2018 -0400
> # Node ID d87ed52203984e979551f7dfd29f906854b5c3c0
> # Parent  93acc58fb2c12c9538cb973cec1b61a308bd84dd
> py3: add b'' to a few strings in pycompat

For this sort of things, you can run "./contrib/byteify-strings.py -i FILE".

I didn't do that for the overall codebase yet since it would generate lots
of merge conflicts. But that's okay for pycompat.py on which nobody would
have working patches.