The fluid circuitry 42 includes a control valve 45 adapted to be actuated manually by a pivotal trigger member 46 for selectively directing fluid, such as compressed air, from the fluid supply conduit 43 to either end portion of the cylinder 40, in order to selectively force the piston 48 (shown in phantom in FIGS. 4 and 5) and the piston rod 39 in a forward (protracted) or rearward (retracted) di