title: Fabric.js: can't get the active groups anymore
body: <p>I'm using fabric 1.4.10 and i noticed that i can't get the active groups anymore! Everytime i call canvas.getActiveGroup() even when a group is selected, i get null.</p>
  
  <p>My code to create groups:</p>
  
  <pre>
  var circle1 = new fabric.Circle({
    radius: 50,
    fill: 'red',
    left: 0
  });
  var circle2 = new fabric.Circle({
    radius: 50,
    fill: 'green',
    left: 100
  });
  var circle3 = new fabric.Circle({
    radius: 50,
    fill: 'blue',
    left: 200
  });
  
  var group = new fabric.Group([ circle1, circle2, circle3 ], {
    left: 200,
    top: 100
  });
  
  canvas.add(group);
  </pre>
  
  <p>Can anyone help please?</p>