[mail] allow to specify SMTP's MAIL FROM address to config.sendmails(). Closes #3373620 Also modify testlib.Email so we don't loose this information and may test it.

#!/bin/sh -e
if [ "$1" = "purge" ] ; then
        update-rc.d cubicweb remove >/dev/null
fi
 
#DEBHELPER#
 
exit 0