bug#23779: 25.0.95; consing "SHELLVAR" onto process-environment doesn't remove it from subprocess env

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Tue, 21 Jun 2016 16:53:40 +0300
> 
> On 06/20/2016 05:21 PM, Eli Zaretskii wrote:
> 
> > OK, thanks.  Pushed as 5f37572 on the emacs-25 branch, and closing.
> 
> Can we fix bug#23769 along with it?
> 
> The solution using process-environment looks obviously safe to me.

Please show a patch you have in mind.