Make args package follow new layout.

utils/pub/pub.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.
 
 /**
  * The main entrypoint for the pub command line application.
  */
 #library('pub');
 
-#import('../../pkg/args/args.dart');
+#import('../../pkg/args/lib/args.dart');
 #import('dart:io');
 #import('dart:math');
 #import('io.dart');
 #import('command_help.dart');
 #import('command_install.dart');
 #import('command_list.dart');
 #import('command_update.dart');
 #import('command_version.dart');
 #import('entrypoint.dart');
 #import('git_source.dart');
@@ skipping 210 matching lines @@
     print('');
     print('Usage: $usage');
 
     var commandUsage = commandParser.getUsage();
     if (!commandUsage.isEmpty()) {
       print('');
       print(commandUsage);
     }
   }
 }