In keeping with Adobe's convention, Set and Map's forEach() function takes an optional 'thisObject' param

git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@5502 542714f4-19e9-0310-aa3c-eee0fc999fb1

src/as/com/threerings/util/ExpiringSet.as

@@ -63,10 +63,10 @@ public class ExpiringSet extends EventDispatcher
     }
 
     // from Set
-    public function forEach (fn :Function) :void
+    public function forEach (fn :Function, thisObject :* = null) :void
     {
         for each (var e :ExpiringElement in _data) {
-            fn(e);
+            fn.call(thisObject, e);
         }
     }