Not sure if anyone has tried this script, or it's worth me putting in on the CHDK scripts page; however, here is the latest version, which adds in exposure bracketing (+/- or -/-- or +/++ around 0Ev) and tidies things up.
The script can be downloaded from here:
https://gist.github.com/pigeonhill/10a43f5ba543bc758f1ce21d28981a89The unit of blur used in the script is the CHDK CoC for the camera.
Thus the overlap choices are none, ie each focus bracket just touches the previous one, or overlaps at 2CcC/3 or CoC/2.
The infinity blur final shot, ie the one taken beyond the hyperfocal, is taken at either CoC/2, CoC/3 or CoC/4.
The script creates a log of the focus positions by default.
As usual I welcome any feedback.