Implement import scope

tests/language/library1_negative_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // This test should fail to load because we are importing two libraries
-// which define the same top level name.  This is an error even if the
-// variable 'foo' is never referred to.
+// which define the same top level name foo, and we are referring to the name.
 
 #library("Library1NegativeTest.dart");
 #import("library1.dart");  // Defines top level variable 'foo'
 #import("library2.dart");  // Defines top level variable 'foo'
 
 
 main() {
-  Expect.equals(0, foo1); // This uses 'foo1' on purpose instead of 'foo'
+  Expect.equals(0, foo); // Reference ambiguous name 'foo'
 }