Have messages know their own formatting string.

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4496 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/crowd/chat/data/ChatMessage.as

@@ -67,6 +67,14 @@ public /*abstract*/ class ChatMessage
         timestamp = getTimer();
     }
 
+    /**
+     * Get the appropriate message format for this message.
+     */
+    public function getFormat () :String
+    {
+        return null;
+    }
+
     /**
      * Generates a string representation of this instance.
      */