Clean up some warnings.

compiler/java/com/google/dart/compiler/resolver/CyclicDeclarationException.java

Index: compiler/java/com/google/dart/compiler/resolver/CyclicDeclarationException.java
===================================================================
--- compiler/java/com/google/dart/compiler/resolver/CyclicDeclarationException.java	(revision 11395)
+++ compiler/java/com/google/dart/compiler/resolver/CyclicDeclarationException.java	(working copy)
@@ -1,4 +1,4 @@
-// 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.
 
@@ -8,6 +8,8 @@
  * Exception thrown if a cycle is detected in the supertype graph of a class or interface.
  */
 public class CyclicDeclarationException extends Exception {
+  private static final long serialVersionUID = 1L;
+
   private final ClassElement element;
 
   public CyclicDeclarationException(ClassElement element) {