Revert "Switch libraries to using new tags."

sdk/lib/core/exceptions.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;
-
 // Exceptions are thrown either by the VM or from Dart code.
 
 /**
  * A marker interface implemented by all core library exceptions.
  *
  * An [Exception] is intended to convey information to the user about a failure,
  * so that the error can be addressed programmatically. It is intended to be
  * caught, and it should contain useful data fields.
  *
  * Creating instances of [Exception] directly with [:new Exception("message"):]
@@ skipping 51 matching lines @@
 }
 
 /**
  * Exception thrown when a runtime error occurs.
  */
 class RuntimeError implements Exception {
   final message;
   RuntimeError(this.message);
   String toString() => "RuntimeError: $message";
 }