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

tests/language/src/Library5b.dart

Index: tests/language/src/Library5b.dart
===================================================================
--- tests/language/src/Library5b.dart	(revision 0)
+++ tests/language/src/Library5b.dart	(revision 0)
@@ -0,0 +1,8 @@
+// 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.
+//
+
+#library("Library5b.dart");
+
+typedef int Fun(x);