FIX: Previous checkin message should say: GradientMagnitudeRecursiveGaussian      filter added. This is the on using IIR for approximating convolution. ENH: Now, really adding the GradientMagnitude filter that uses finite differences.
FIX: Previous checkin message should say: GradientMagnitudeRecursiveGaussian
     filter added. This is the on using IIR for approximating convolution.
ENH: Now, really adding the GradientMagnitude filter that uses finite differences.

aylward/ImageViewer,thewtex/ImageViewer,KitwareMedical/ImageViewer