PGM to OpenSCAD surface (normed zero-one)

This is a "normed" version of the original. which means this script makes a ".dat" file with grey scales (0-255) converted to (0.00-1.00). This works a lot better if you are going to upload your openSCAD code to thingivese customizer. NOTE: I am not a python expert I just used trial and error to assign the correct value to depthval. If you have python questions I probably can not answer them, @sawdusty is the master here. http://www.thingiverse.com/thing:75581

The original makes a ".dat" file with grey scales (0-255) converted to (0.00-7.65) which is fine..but is not compatible with how thingiverse works.

http://customizer.makerbot.com/image_surface
http://customizer.makerbot.com/docs#image_surface

ALSO note in openSCAD the surface command adds 1mm to the bottom (below zero) of the surface it creates