Direction cleaning

Added precompiler directives so that it doesn't compile experiment stuff
on analysis machines, and added a function to constrain the displacement
signal to have only 1nm, 10nm, etc. steps.  Also added AFM calibration
routine from snap-to-contact bits.
Merge branch 'master' of https://github.com/asanders/igor-pro

Conflicts:
	tip_experiment/tip_exp_methods/optical_forces.ipf