Move core and coreimpl from corelib/ to lib/core and lib/coreimpl.

corelib/src/implementation/exceptions.dart

Index: corelib/src/implementation/exceptions.dart
diff --git a/corelib/src/implementation/exceptions.dart b/corelib/src/implementation/exceptions.dart
deleted file mode 100644
index c2dd3a2f4df3754d168a340d568f1eee2b9ee756..0000000000000000000000000000000000000000
--- a/corelib/src/implementation/exceptions.dart
+++ /dev/null
@@ -1,9 +0,0 @@
-// Copyright (c) 2011, 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.
-
-class ExceptionImplementation implements Exception {
-  const ExceptionImplementation([msg = null]) : _msg = msg;
-  String toString() => (_msg === null) ? "Exception" : "Exception: $_msg";
-  final _msg;
-}