Move exit from the builtin library to dart:io.

runtime/bin/builtin.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.
 
 #library("builtin");
 #import("dart:uri");
 
 void print(arg) {
   _Logger._printString(arg.toString());
 }
 
-void exit(int status) {
-  if (status is !int) {
-    throw new IllegalArgumentException("int status expected");
-  }
-  _exit(status);
-}
-
-_exit(int status) native "Exit";
-
 class _Logger {
   static void _printString(String s) native "Logger_PrintString";
 }
 
 
 // The URI that the entrypoint script was loaded from. Remembered so that
 // package imports can be resolved relative to it.
 var _entrypoint;
 
 // The directory to look in to resolve "package:" scheme URIs.
@@ skipping 125 matching lines @@
   var path;
   if (_packageRoot !== null) {
     path = "${_packageRoot}${uri.path}";
   } else {
     path = _entrypoint.resolve('packages/${uri.path}').path;
   }
 
   _logResolution("# Package: $path");
   return path;
 }