title: AndEngine SetAlpha does not Effect child Entity
body: <p>I'm having trouble setting Alpha on a child entity.
  I create a Rectangle entity and attach a Text entity to the rectangle like this:</p>
  
  <pre><code>m_background = new Rectangle(0.0f, 0.0f, m_activity.getCamera().getWidth(), m_activity.getCamera().getHeight(), m_activity.getVertexBufferObjectManager());
  m_background.setColor(0.0f, 0.0f, 0.0f);
  
  FontFactory.setAssetBasePath("font/");
  
  final ITexture fontTexture = new BitmapTextureAtlas(m_activity.getTextureManager(), 256, 256, TextureOptions.BILINEAR);
  this.m_Font = FontFactory.createFromAsset(m_activity.getFontManager(), fontTexture, m_activity.getAssets(), "Droid.ttf", 48, true, android.graphics.Color.WHITE);
  this.m_Font.load();
  
  Text text = new Text(100, 300, this.m_Font, "LoadingScreen", new TextOptions(HorizontalAlign.RIGHT), m_activity.getVertexBufferObjectManager());
      m_background.attachChild(text);
  </code></pre>
  
  <p>Now I want to set the Alpha of this background entity to 0:</p>
  
  <pre><code>m_background.setAlpha(0.0f);
  </code></pre>
  
  <p>I was under the impression that the child entities would be affected as well, is that not the case? How could I do this except by setting alpha directly on the child entities? Is there a better way?</p>
  
  <p>Thanks in advance,
  Zerd</p>