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

tests/language/src/Library5Test.dart

Index: tests/language/src/Library5Test.dart
===================================================================
--- tests/language/src/Library5Test.dart	(revision 0)
+++ tests/language/src/Library5Test.dart	(revision 0)
@@ -0,0 +1,21 @@
+// 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", prefix : "lib5a");
+#import("Library5b.dart", prefix : "lib5b");
+
+int foo(lib5a.Fun f) {
+  return f();
+}
+
+int bar(lib5b.Fun f) {
+  return f(42);
+}
+
+main() {
+  Expect.equals(41, foo(() => 41));
+  Expect.equals(42, bar((x) => x));
+}
+