title: seekbar customization: progress and secondaryProgress property not stretch pictures default
body: <p>I customize my seekbar like below:</p>
  
  <pre><code>&lt;SeekBar android:id="@+id/progress_seekbar" android:background="@drawable/play_progress_bg"
      android:layout_centerHorizontal="true" android:layout_width="fill_parent"
      android:layout_height="wrap_content" android:layout_marginBottom="-9dp"
      android:layout_above="@id/playwidget" android:progressDrawable="@drawable/progress_seekbar_style"
      android:thumb="@drawable/thumb_progress" /&gt;
  </code></pre>
  
  <p>in my progress_seekbar_style.xml file, I specified it like this:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;layer-list xmlns:android="http://schemas.android.com/apk/res/android"&gt;
      &lt;item android:id="@android:id/background" android:drawable="@drawable/play_progress_01" /&gt;
      &lt;item android:id="@android:id/secondaryProgress" android:drawable="@drawable/play_progress_02" /&gt;
      &lt;item android:id="@android:id/progress" android:drawable="@drawable/play_progress_03"/&gt;
  &lt;/layer-list&gt;
  </code></pre>
  
  <p>I want to use this seekbar customization for different screen size; but when it display on the large screen like 600x1024, the seekbar will repeat the picture which I set in "@android:id/background,secondaryProgress/progress " , not stretch my pictures. and I need it automatically stretch my picture to fill parent width. that is what I want, but it just repeat the picture.</p>
  
  <p>can you help? thanks.</p>