a4000 - don't default to using exmem, fixes corrupt jpegs
Fix OSD bug reported by srsa_4c:
http://chdk.setepontos.com/index.php?topic=265.msg106637#msg106637
correct aperture table for a410, a420, a430, a460, ixus30_sd200, ixus40_sd300, ixus65_sd630 - data is based on EXIF values and propcase readings
define CAM_DRAW_EXPOSITION for ixus30_sd200, ixus40_sd300