title: onSharedPreferenceChanged() never called after a clear()
body: <p>I'm experiencing a strange behaviour with SharedPreferences and its listener.
  I use only one SharedPreference instance in my app that I retrieve with <code>PreferenceManager.getDefaultSharedPreferences(this);</code></p>
  
  <p>In my PreferenceFragment, I have a button to reset the preference to default. That's what it does:</p>
  
  <pre><code>PreferenceManager.getDefaultSharedPreferences(getActivity()).edit().clear().commit();
  PreferenceManager.setDefaultValues(getActivity(), R.xml.settings, true);
  </code></pre>
  
  <p>I have several listeners for this SharedPreference. They all work perfectly on addition/modification of my keys. But <strong>they never get fired</strong> on a reset. The doc isn't specific about this case, but states:</p>
  
  <blockquote>
    <p><em>onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key)</em></p>
    
    <p>Called when a shared preference is changed, added, or removed.</p>
  </blockquote>
  
  <p>And for me a reset is a removal of all preferences, so I'm expecting it the callback to happen.</p>
  
  <p>Why doesn't it happen?
  Thanks a lot!</p>