improve cleanup of VCA related objects

libs/ardour/route.cc

@@ -5442,6 +5442,8 @@ Route::slaved_to (boost::shared_ptr<VCA> vca) const
 		return false;
 	}
 
+	/* just test one particular control, not all of them */
+
 	return _gain_control->slaved_to (vca->gain_control());
 }
 

libs/ardour/slavable_automation_control.cc

@@ -139,7 +139,7 @@ SlavableAutomationControl::add_master (boost::shared_ptr<AutomationControl> m)
 			   itself.
 			*/
 
-			m->DropReferences.connect_same_thread (masters_connections, boost::bind (&SlavableAutomationControl::master_going_away, this, m));
+			m->DropReferences.connect_same_thread (masters_connections, boost::bind (&SlavableAutomationControl::master_going_away, this, boost::weak_ptr<AutomationControl>(m)));
 
 			/* Store the connection inside the MasterRecord, so that when we destroy it, the connection is destroyed
 			   and we no longer hear about changes to the AutomationControl.
@@ -242,6 +242,7 @@ SlavableAutomationControl::remove_master (boost::shared_ptr<AutomationControl> m
 
 	pre_remove_master (m);
 
+
 	{
 		Glib::Threads::RWLock::WriterLock lm (master_lock);
 		current_value = get_value_locked ();

libs/ardour/vca_manager.cc

@@ -48,6 +48,9 @@ void
 VCAManager::clear ()
 {
 	Mutex::Lock lm (lock);
+	for (VCAList::const_iterator i = _vcas.begin(); i != _vcas.end(); ++i) {
+		(*i)->DropReferences ();
+	}
 	_vcas.clear ();
 }