The connection was stored by the Port where it was initiated from:
1. Connect A to B
2. Disconnect B from A
(1) Port A remembers the connection to B
(2) Port B does not know about the connection from A
Since disconnect is initiated on port B, port A still retained
the connection information.
When restarting the engine, Port::reconnect() reestablished the
connection.
This is only relevant when libardour's own connection information is
used. e.g. the session is closed without engine, or when re-starting
the engine while the session is open.
786388b5b6