Clean up some warnings.

editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/DartModelException.java

Index: editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/DartModelException.java
===================================================================
--- editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/DartModelException.java	(revision 11395)
+++ editor/tools/plugins/com.google.dart.tools.core/src/com/google/dart/tools/core/model/DartModelException.java	(working copy)
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2011, the Dart project authors.
+ * Copyright (c) 2012, the Dart project authors.
  * 
  * Licensed under the Eclipse Public License v1.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
@@ -27,6 +27,8 @@
  * exception.
  */
 public class DartModelException extends CoreException {
+  private static final long serialVersionUID = 1L;
+
   /**
    * The code exception that caused this model exception, or <code>null</code> if this exception was
    * not caused by a model exception.