Revert "Switch libraries to using new tags."

sdk/lib/core/errors.dart

 // 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.
 
-part of dart.core;
-
 class Error {
   const Error();
 
   /**
    * Safely convert a value to a [String] description.
    *
    * The conversion is guaranteed to not throw, so it won't use the object's
    * toString method.
    */
   static String safeToString(Object object) {
@@ skipping 53 matching lines @@
 
   String toString() {
     if (message != null) {
       return "Illegal argument(s): $message";
     }
     return "Illegal argument(s)";
   }
 }
 
 /**
- * Error thrown because of an index outside of the valid range.
+ * Exception thrown because of an index outside of the valid range.
  *
  */
 class RangeError extends ArgumentError {
   // TODO(lrn): This constructor should be called only with string values.
   // It currently isn't in all cases.
   /**
    * Create a new [RangeError] with the given [message].
    *
    * Temporarily made const for backwards compatibilty.
    */
@@ skipping 158 matching lines @@
 }
 
 /**
  * Error thrown when a runtime error occurs.
  */
 class RuntimeError implements Error {
   final message;
   RuntimeError(this.message);
   String toString() => "RuntimeError: $message";
 }