title: Can't retain nested fragments
body: <p>Is there another way of saving the state of the nested fragment ? 
  Or if we shouldn't do this, why ? Thanks !</p>
  
  <pre><code>02-13 11:42:43.258: E/AndroidRuntime(7167): java.lang.IllegalStateException: Can't retain fragements that are nested in other fragments
  02-13 11:42:43.258: E/AndroidRuntime(7167):     at android.support.v4.app.Fragment.setRetainInstance(Fragment.java:742)
  </code></pre>