Fixes jashkenas#733 -- quick-fix implementation of isEqual on naked o…

…bjects from different frames.

test/objects.js

@@ -342,6 +342,9 @@ $(document).ready(function() {
     ok(_.isEqual(isEqualObjClone, isEqualObj), 'Commutative equality is implemented for objects with custom `isEqual` methods');
     ok(!_.isEqual(isEqualObj, {}), 'Objects that do not implement equivalent `isEqual` methods are not equal');
     ok(!_.isEqual({}, isEqualObj), 'Commutative equality is implemented for objects with different `isEqual` methods');
+
+    // Objects from another frame.
+    ok(_.isEqual({}, iObject));
   });
 
   test("isEmpty", function() {
@@ -378,6 +381,7 @@ $(document).ready(function() {
       parent.iNull      = null;\
       parent.iBoolean   = new Boolean(false);\
       parent.iUndefined = undefined;\
+      parent.iObject     = {};\
     </script>"
   );
   iDoc.close();

underscore.js

@@ -847,8 +847,13 @@
         }
       }
     } else {
-      // Objects with different constructors are not equivalent.
-      if ('constructor' in a != 'constructor' in b || a.constructor != b.constructor) return false;
+      // Objects with different constructors are not equivalent, but `Object`s
+      // from different frames are.
+      var aCtor = a.constructor, bCtor = b.constructor;
+      if (aCtor !== bCtor && !(_.isFunction(aCtor) && (aCtor instanceof aCtor) &&
+                               _.isFunction(bCtor) && (bCtor instanceof bCtor))) {
+        return false;
+      }
       // Deep compare objects.
       for (var key in a) {
         if (_.has(a, key)) {