bugs with delivery muting. The upshot being that muting now definitely
happens in a channel's deliveries, and not really in the channel strip
at all. When the channel is muted, those deliveries described by
the MuteMaster settings are muted. Should fix#3141.
git-svn-id: svn://localhost/ardour2/branches/3.0@7115 d708f5d6-7413-0410-9779-e7cbd77b26cf