[vtkusers] Change in cropping region planes

[Lisa S. Avila]

Hello,

I just checked a change in for VTK 4.0 that changes the definition of the 
cropping region planes in volume rendering. Previously they were defined in 
"voxel" coordinates (ranging from 0 to dim[i]-1 for each of the 3 axes). 
Now they are defined in "volume" coordinates (ranging from origin[i] to 
(origin[i] + (dim[i]-1)*spacing[i]) for each of the 3 axes.)

Let me know if you run into any problems.

Lisa