Allow the chat-clearing behavior to be overridden.

On msoy you "log off" when you switch servers, which I think
we need to change, but... that's a bigger change.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@5294 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/crowd/chat/client/ChatDirector.as

@@ -619,7 +619,7 @@ public class ChatDirector extends BasicDirector
         removeAuxiliarySource(_clobj);
         addAuxiliarySource(_clobj = event.getClient().getClientObject(), ChatCodes.USER_CHAT_TYPE);
 
-        clearDisplays();
+        clientLeftOrChanged();
     }
 
     // documentation inherited
@@ -635,8 +635,6 @@ public class ChatDirector extends BasicDirector
         // in fact, clear out all auxiliary sources
         _auxes.clear();
 
-        clearDisplays();
-
         // clear out the list of people we've chatted with
         _chatters.length = 0;
         notifyChatterObservers();
@@ -646,6 +644,16 @@ public class ChatDirector extends BasicDirector
 
         // clear our service
         _cservice = null;
+
+        clientLeftOrChanged();
+    }
+
+    /**
+     * Overridable.
+     */
+    protected function clientLeftOrChanged () :void
+    {
+        clearDisplays();
     }
 
     /**