closing out Library*NegativeTest issue and adding comments

tests/language/src/Library4NegativeTest.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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. In this case libraryE.dart is
-// importing libraryC.dart and libraryF.dart which both define variable
-// "fooC".
+// This test should fail to load because library1 defines a top-level
+// variable named 'foo' which conflicts with the prefix 'foo' used to import
+// library3.  This is an error even if 'foo' is never referred to.
 
 #library("Library4NegativeTest.dart");
-#import("library1.dart");
-#import("library3.dart", prefix:"foo");
+#import("library1.dart"); // Defines a top-level variable 'foo'
+#import("library3.dart", prefix:"foo"); // Creates prefix 'foo'
 
 main() {
 }