Put collision state for a particular block.
        Any operations checked at this block_id that collide 
        with the given collision state will be rejected.

def put_collisions( self, block_id, collisions ):
        """
        Put collision state for a particular block.
        Any operations checked at this block_id that collide 
        with the given collision state will be rejected.
        """
        self.collisions[ block_id ] = copy.deepcopy( collisions )