-------------------------------------------
variable: $norm_move_mm_or_frac -- dist along normal
-------------------------------------------
default: -0.5

Set distance to move each vertex along vertex
normal for a single click of the "N" button.
Positive is outward, negative inward.

This can be used to make subvoxel adjustments to
the extent of the 3D fill_surface operation.

A middle-click on the "N" button uses fraction of
cortical thickness at each vertex instead of the
default mm.
