Import io.dart in pub.dart.

Review URL: https://codereview.chromium.org//14261016

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@21994 260f80e4-7a28-3924-810f-c04153c831b5

bin/pub.dart

@@ -11,6 +11,7 @@ import 'package:pathos/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/system_cache.dart';