Fix buffer size issue.
Motion detection updates from waterwingz:
http://chdk.setepontos.com/index.php?topic=650.msg96967#msg96967
http://chdk.setepontos.com/index.php?topic=650.msg97003#msg97003
Motion detect AF LED test update for A720, SX220 & SX230 from msl:
http://chdk.setepontos.com/index.php?topic=9366.msg97032#msg97032