Roll Observatory packages and add a roll script

packages/watcher/example/watch.dart

Index: packages/watcher/example/watch.dart
diff --git a/packages/watcher/example/watch.dart b/packages/watcher/example/watch.dart
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+// 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.
+
+/// Watches the given directory and prints each modification to it.
+library watch;
+
+import 'package:path/path.dart' as p;
+import 'package:watcher/watcher.dart';
+
+main(List<String> arguments) {
+  if (arguments.length != 1) {
+    print("Usage: watch <directory path>");
+    return;
+  }
+
+  var watcher = new DirectoryWatcher(p.absolute(arguments[0]));
+  watcher.events.listen((event) {
+    print(event);
+  });
+}