different types of port; if we loop over N MIDI channels of
a mixed bundle, for example, we must convert 0...N to the
indices of the channels within the bundle. Also remove the
hack of creating new bundles to contain a subset of another
bundle's ports; if you do this, any signals emitted by the
other bundle are ignored. Should fix#4454.
git-svn-id: svn://localhost/ardour2/branches/3.0@10490 d708f5d6-7413-0410-9779-e7cbd77b26cf