[TIMOB-5803] iOS: Button background image does not scale correctly on click

When the image used by a button is larger than the size of the button, the image will correctly scale down to fit the button when the button is in the normal state. However, when the button is in the "pressed" state, the backgroundImage no longer scales correctly.

var win = Titanium.UI.currentWindow;
var button = Titanium.UI.createButton({
  height:60,
  width:80,
  backgroundImage:'slightlylargerimage.png'
});
win.add(button);