Fix wrong detection of duplicate definition of function types (issue 187).

tests/language/src/Library5NegativeTest.dart

Index: tests/language/src/Library5NegativeTest.dart
===================================================================
--- tests/language/src/Library5NegativeTest.dart	(revision 0)
+++ tests/language/src/Library5NegativeTest.dart	(revision 0)
@@ -0,0 +1,10 @@
+// Copyright (c) 2011, 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.
+//
+
+#import("Library5a.dart");
+#import("Library5b.dart");  // The function type alias Fun is duplicated.
+
+main() {
+}