title: FileSystemWatcher raised event twice
body: <pre><code>public void startWatch()
  {
      FileSystemWatcher watcher = new FileSystemWatcher();
      watcher.Path = Path.GetDirectoryName(_file);
      watcher.Filter = Path.GetFileName(_file);
      watcher.NotifyFilter = NotifyFilters.LastWrite;
      watcher.Changed += watcher_Changed;
      watcher.EnableRaisingEvents = true;
  }
  
  public void watcher_Changed(object sender, FileSystemEventArgs e)
  {
      // Jump twice
  }
  </code></pre>
  
  <p>Why this event jump twice after my text file changed?</p>