Fix proposed-updates handling in byhand-di and byhand-win32-loader

To: debian-dak@lists.debian.org
Cc: kibi@debian.org, Julien Cristau <jcristau@debian.org>
Date: Tue, 19 Jan 2016 11:40:01 +0100 (12 hours, 2 minutes, 47 seconds ago)
Resent-From: debian-dak@lists.debian.org

stable-proposed-updates is called "proposed-updates" in projectb, so
that's what we pass to the byhand script.  It shouldn't be turned into
"proposed-updates-proposed-updates".

Signed-off-by: Julien Cristau <jcristau@debian.org>