closing out Library*NegativeTest issue and adding comments

tests/language/src/Library5NegativeTest.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 tests that it is a compile-time error to import two libraries that
+// both define a function type alias with the same name.
+// This name conflict is considered an error even if Fun is never referred to.
 
 #library("Library5NegativeTest.dart");
-#import("Library5a.dart");
-#import("Library5b.dart");  // The function type alias Fun is duplicated.
+#import("Library5a.dart");  // Defines function type alias Fun
+#import("Library5b.dart");  // Also defines function type alias Fun
 
 main() {
 }