title: How to change boundingbox size in cocos2d
body: <p>I'm making a cocos2d game where I need to have a ball shaped sprite that is 140x140, but i want it's bounding box to be only 70x70 in size, so that only the center of the ball collides. If tried to edit the bounding box's size after the sprite is created, but it looks like the boundingbox property is not assignable. I've also tried to specify the rect in the constructor using <code>initWithFile:rect:</code> but then the sprite is cut and only the colliding part is drawn, and I want the whole sprite to be drawn, but just the center of it to be reacting to collisions. Is it possible to do this via boundingbox or is this property directly bound to the size of the drawn sprite?</p>