[PATCH 1 of 6 py3] config: add sanity assert that files are opened as binary

[Yuya Nishihara]

On Mon, 06 Mar 2017 18:23:05 -0500, Augie Fackler wrote:
> # HG changeset patch
> # User Augie Fackler <raf at durin42.com>
> # Date 1488563711 18000
> #      Fri Mar 03 12:55:11 2017 -0500
> # Node ID 428615d799a9115249f3aab8d6481e384e879f6a
> # Parent  41a9edc5d00f2b5744e1edaf2edaa10084099f53
> config: add sanity assert that files are opened as binary

Fixed minor nits and queued the series, thanks.