being logged before they are handled, and to invalidate them all rather
than just the last one. Fixes shutdown problems when the PortMatrix has
been opened during the session, during which PortRegisteredOrUnregistered
is emitted quite heavily.
git-svn-id: svn://localhost/ardour2/branches/3.0@6852 d708f5d6-7413-0410-9779-e7cbd77b26cf