[PATCH 2 of 9 V2] py3: don't use os.getcwdb() on Windows to avoid DeprecationWarnings

[Yuya Nishihara]

On Mon, 24 Sep 2018 22:25:35 -0400, Matt Harbison wrote:
> # HG changeset patch
> # User Matt Harbison <matt_harbison at yahoo.com>
> # Date 1537756604 14400
> #      Sun Sep 23 22:36:44 2018 -0400
> # Node ID bf1934083fa5c3a97492ea112ddb23e8ccf78294
> # Parent  1fcff747a558e32f9cb9d8411c256532455c10f8
> py3: don't use os.getcwdb() on Windows to avoid DeprecationWarnings

Queued the series, thanks.

> +    if pycompat.osname == b'nt':

Replaced this with pycompat.iswindows.