Fix a number of issues with determining the type of stdio

tests/standalone/io/dart_std_io_pipe_script.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.
 //
 // Utility script to echo stdin to stdout or stderr or both.
 
 import "dart:io";
 
 main() {
   var options = new Options();
+  if (stdioType(stdin) is !StdioType) exit(1);
+  if (stdioType(stdout) is !StdioType) exit(1);
+  if (stdioType(stderr) is !StdioType) exit(1);
+  if (stdioType(stdin).name != options.arguments[1]) {
+    throw stdioType(stdin).name;
+  }
+  if (stdioType(stdout).name != options.arguments[2]) {
+    throw stdioType(stdout).name;
+  }
+  if (stdioType(stderr).name != options.arguments[3]) {
+    throw stdioType(stderr).name;
+  }
   if (options.arguments.length > 0) {
     if (options.arguments[0] == "0") {
       stdin.pipe(stdout);
     } else if (options.arguments[0] == "1") {
       stdin.pipe(stderr);
     } else if (options.arguments[0] == "2") {
       stdin.listen((data) {
         stdout.writeBytes(data);
         stderr.writeBytes(data);
       });
     }
   }
 }