Support directories other than "web" in pub build.

sdk/lib/_internal/pub/bin/pub.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.
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
 import 'package:path/path.dart' as path;
 
 import '../lib/src/command.dart';
 import '../lib/src/exit_codes.dart' as exit_codes;
 import '../lib/src/io.dart';
 import '../lib/src/log.dart' as log;
 import '../lib/src/sdk.dart' as sdk;
 import '../lib/src/utils.dart';
 
 void main(List<String> arguments) {
   ArgResults options;
 
   try {
-    options = PubCommand.pubArgParser.parse(arguments);
+    options = PubCommand.pubArgParser.parse(arguments,
+        allowTrailingOptions: true);
   } on FormatException catch (e) {
     log.error(e.message);
     log.error('Run "pub help" to see available options.');
     flushThenExit(exit_codes.USAGE);
     return;
   }
 
   if (options['version']) {
     log.message('Pub ${sdk.version}');
     return;
@@ skipping 59 matching lines @@
     if (Platform.operatingSystem != 'windows') return null;
 
     return runProcess('ver', []).then((result) {
       if (result.stdout.join('\n').contains('XP')) {
         log.error('Sorry, but pub is not supported on Windows XP.');
         return flushThenExit(exit_codes.USAGE);
       }
     });
   });
 }