title: createjs mask a Bitmap with another Bitmap
body: <p>I'm trying to mask a <a href="http://createjs.com/docs/easeljs/classes/Bitmap.html" rel="nofollow">Bitmap</a> object with another <code>Bitmap</code>, but so far with actual success.<br>
  There's a <a href="http://jsfiddle.net/lannymcnie/T8ukz/2/" rel="nofollow">jsfiddle by Lanny</a>, but it involves a <a href="http://createjs.com/docs/easeljs/classes/Shape.html" rel="nofollow">Shape</a> object being the mask, so my questions are:<br></p>
  
  <ol>
  <li>Can you use an alpha channel from another bitmap to mask a createjs <code>Bitmap</code> object?</li>
  <li>Is it possible to use an alpha channel from a png image as a mask?</li>
  </ol>