Made the map work with null as a key.

(Dictionary supports null keys, so we merely call null a 'simple' key.)


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@4848 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/util/HashMap.as

@@ -313,7 +313,7 @@ public class HashMap
      */
     protected function isSimple (key :Object) :Boolean
     {
-        return (key is String) || (key is Number) || (key is Boolean);
+        return (key == null) || (key is String) || (key is Number) || (key is Boolean);
     }
 
     /**