A810, A1400: Use Video button as Display button
A1300: Use Video button as Display button
Fix #undef CAM_HAS_DISP_BUTTON (A2300, A2400, A3400, A4000, A470, D20, IXUS1000, IXUS300)
revert to old PROPCASE_SHOOTING for propset 2, see http://chdk.setepontos.com/index.php?topic=11604.msg114050#msg114050