Make pub use the SDK's "version" file for its version.

utils/tests/pub/update/pub_update_test.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 pub_tests;
 
 import 'dart:io';
 
 import '../../../../pkg/unittest/lib/unittest.dart';
 import '../test_pub.dart';
@@ skipping 51 matching lines @@
 
     dir(packagesPath, [
       nothing("myapp_name")
     ]).scheduleValidate();
   });
 
   integration('does not add a package if it does not have a "lib" '
       'directory', () {
     // Using an SDK source, but this should be true of all sources.
     dir(sdkPath, [
-      file('revision', '1234'),
+      file('version', '0.1.2.3'),
       dir('pkg', [
         dir('foo', [
           libPubspec('foo', '0.0.0-not.used')
         ])
       ])
     ]).scheduleCreate();
 
     dir(appPath, [
       pubspec({"name": "myapp", "dependencies": {"foo": {"sdk": "foo"}}})
     ]).scheduleCreate();
 
     schedulePub(args: ['update'],
         output: new RegExp(r"Dependencies updated!$"));
 
     packagesDir({"foo": null}).scheduleValidate();
   });
 }