Deregister agent event handlers on window close

Previously we only deregistered window update listeners when the corresponding
agent was destroyed; possibly it was never tested what would happen when a
single agent window was closed while leaving the agent alive.

Fixes #431.

Java/Debugger/src/edu/umich/soar/debugger/MainFrame.java

@@ -393,14 +393,14 @@ private void thisWindowClosing()
         m_bClosing = true;
 
         // Need to explicitly release the focus which in turn will cause any
-        // listeners to unregister from this agent (is its still alive).
+        // listeners to unregister from this agent (if it's still alive).
         // Otherwise our listeners will
         // still be registered and will try to display output in windows that
         // are disposed.
         // This has the potential to deadlock (waiting to issue unregister calls
         // while we're running) so we put
         // it in a separate thread to avoid that.
-        Thread clearFocus = new Thread(() -> clearAgentFocus(false));
+        Thread clearFocus = new Thread(() -> clearAgentFocus(true));
         clearFocus.start();
 
         // DJP: Experiment