Reapply conversion of most core interfaces to abstract classes.

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.
 
 // Exceptions are thrown either by the VM or from Dart code.
 
 /**
  * Interface implemented by all core library exceptions.
+ * Defaults to an implementation that only carries a simple message.
  */
 interface Exception default ExceptionImplementation {
-  const Exception([var msg]);
+  const Exception([var message]);
 }
 
 
 /**
  * Exception thrown because of an index outside of the valid range.
  */
 class IndexOutOfRangeException implements Exception {
   const IndexOutOfRangeException(this._value);
 
   String toString() => "IndexOutOfRangeException: $_value";
@@ skipping 128 matching lines @@
 }
 
 /**
  * Exception thrown when a runtime error occurs.
  */
 class RuntimeError implements Exception {
   final message;
   RuntimeError(this.message);
   String toString() => "RuntimeError: $message";
 }