Fix extraction of environment variables on Windows.

tests/standalone/io/windows_environment_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.
+
+#import("dart:io");
+
+main() {
+  if (Platform.operatingSystem != 'windows') return;
+  var tempDir = new Directory('').createTempSync();
+  var funkyDir = new Directory("${tempDir.path}/å");
+  funkyDir.createSync();
+  var funkyFile = new File('${funkyDir.path}/funky.bat');
+  funkyFile.writeAsStringSync("""
+@echo off
+set SCRIPTDIR=%~dp0
+%1 %2
+      """);
+  var options = new Options();
+  var dart = options.executable;
+  var scriptDir = new Path.fromNative(options.script).directoryPath;
+  var script = scriptDir.append('windows_environment_script.dart');
+  Process.run('cmd',
+              ['/c', funkyFile.name, dart, script.toNativePath()]).then((p) {
+    Expect.equals(0, p.exitCode);
+    tempDir.deleteSync(recursive: true);
+  });
+}