Update pkg/path to use "package:" imports.

pkg/path/test/path_posix_test.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.
 
 library path_test;
 
 import 'dart:io' as io;
 
-// TODO(rnystrom): Use "package:" path when #7491 is fixed.
-import '../../unittest/lib/unittest.dart';
-import '../lib/path.dart' as path;
+import 'package:unittest/unittest.dart';
+import 'package:path/path.dart' as path;
 
 main() {
   var builder = new path.Builder(style: path.Style.posix, root: '/root/path');
 
   if (new path.Builder().style == path.Style.posix) {
     group('absolute', () {
       expect(path.absolute('a/b.txt'), path.join(path.current, 'a/b.txt'));
       expect(path.absolute('/a/b.txt'), '/a/b.txt');
     });
   }
@@ skipping 343 matching lines @@
     expect(builder.withoutExtension('a/.'), 'a/.');
     expect(builder.withoutExtension('a/.b'), 'a/.b');
     expect(builder.withoutExtension('a.b/c'), 'a.b/c');
     expect(builder.withoutExtension(r'a.b\c'), r'a');
     expect(builder.withoutExtension(r'a/b\c'), r'a/b\c');
     expect(builder.withoutExtension(r'a/b\c.d'), r'a/b\c');
     expect(builder.withoutExtension('a/b.c/'), 'a/b/');
     expect(builder.withoutExtension('a/b.c//'), 'a/b//');
   });
 }