Rename "pathos" package to "path".

pkg/pathos/test/pathos_io_test.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:io' as io;
-
-import 'package:unittest/unittest.dart';
-import 'package:pathos/path.dart' as path;
-
-main() {
-  group('new Builder()', () {
-    test('uses the current working directory if root is omitted', () {
-      var builder = new path.Builder();
-      expect(builder.root, io.Directory.current.path);
-    });
-
-    test('uses the host OS if style is omitted', () {
-      var builder = new path.Builder();
-      if (io.Platform.operatingSystem == 'windows') {
-        expect(builder.style, path.Style.windows);
-      } else {
-        expect(builder.style, path.Style.posix);
-      }
-    });
-  });
-
-  test('current', () {
-    expect(path.current, io.Directory.current.path);
-  });
-}