Fix test.py and tests to use an explicit --packages flag.

tests/standalone/io/skipping_dart2js_compilations_test.dart

 // Copyright (c) 2013, 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.
 
 /*
  * This test makes sure that the "skipping Dart2Js compilations if the output is
  * already up to date" feature does work as it should.
  * Therefore this test ensures that compilations are only skipped if the last
  * modified date of the output of a dart2js compilation is newer than
  *   - the dart application to compile (including it's dependencies)
@@ skipping 147 matching lines @@
   return runner.CommandBuilder.instance.getCompilationCommand(
       'dart2js',
       fileUtils.testJsFilePath.toNativePath(),
       false,
       bootstrapDeps,
       executable,
       arguments, {});
 }
 
 void main() {
+  // This script is in [sdk]/tests/standalone/io.
+  suite.TestUtils.setDartDirUri(Platform.script.resolve('../../..'));
+
   var fs_noTestJs = new FileUtils(createJs: false,
                                   createJsDeps: true,
                                   createDart: true,
                                   createSnapshot: true);
   var fs_noTestJsDeps = new FileUtils(createJs: true,
                                       createJsDeps: false,
                                       createDart: true,
                                       createSnapshot: true);
   var fs_noTestDart = new FileUtils(createJs: true,
                                     createJsDeps: true,
@@ skipping 59 matching lines @@
       cleanup();
       throw error;
     }).then((_) {
       cleanup();
     });
   }
   // We need to wait some time to make sure that the files we 'touch' get a
   // bigger timestamp than the old ones
   new Timer(new Duration(seconds: 1), touchFilesAndRunTests);
 }