title: ImageButton doesn't highlight on click with Transparent background
body: <p>I've set up an ImageButton to be transparent, so the icon matches the backgrond panel like the Android ActionBar. This looks fine as I want it to.</p>
  
  <p>However, when the background is transparent, there isn't the blueish highlight you see as when you press a transparent button in the action bar.</p>
  
  <p>Can I have an ImageButton that is transparent and also has the highlight flash when clicked?</p>
  
  <pre><code>&lt;ImageButton
      android:id="@+id/nextItemButton"
      style="?android:attr/buttonStyleSmall"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_alignParentRight="true"
      android:layout_alignParentTop="true"
      android:background="@null"
      android:src="@drawable/ic_media_ff" /&gt;
  </code></pre>