Use "package:" imports for pub.

test/global/list_test.dart

 // Copyright (c) 2014, 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 'package:path/path.dart' as p;
+import 'package:pub/src/io.dart';
 
-import '../../lib/src/io.dart';
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
 
   integration('lists an activated hosted package', () {
     servePackages((builder) {
       builder.serve('foo', '1.0.0');
     });
@@ skipping 49 matching lines @@
 aaa 1.0.0
 bbb 1.0.0
 ccc 1.0.0
 ''');
   });
 
   integration('lists nothing when no packages activated', () {
     schedulePub(args: ['global', 'list'], output: '\n');
   });
 }