initial subject distance (focus) override rework from waterwingz in http://chdk.setepontos.com/index.php?topic=11078.msg110805#msg110805
This is intended to address many longstanding issues with sd override. There are significant changes from 1.2 behavior and probably bugs - please use the forum thread to report any issues
* enables almost all cameras to override subject distance
* adds set_mf() script function to enter MF mode, even on cameras without MF
* set aflock property case when entering aflock
* if in aflock, script sd override takes effect immediately like for mf
* #defines related to sd override are simplified
don't allow sd override in servo or continuous, unless the camera is in aflock or mf
update ixus132_elph115 for sd override changes to fix build (no sd override methods defined)
add waterwingz mf test script, renamed to mftest, log renamed to mf_<camera>.csv