OBJ_I_INVIS             If this property is set the object is invisible.
                        It should be set to 1 in normal objects and to 100
                        in wizards. Wizards and players that see invis
                        will see this object like '(<short_desc>)' instead.
                        If you want an object that is 'non existant', invis
                        for both players and wizards, use set_no_show().

