The output of StressField is actually the deviatoric stress, so it has already
had the pressure subtracted out.  The documentation is misleading as it does not
mention this.  The best fix is to rename StoreStress to StoreDeviatoricStress
and StressField to DeviatoricStressField.

There seems top be some discrepancy btwn. Pressure and Stress tensor output. 
The normal stress cmpts (Sxx Syy Szz) at nodes do not jive with pressure at
adjacent element centers.  Attached is input and outputs for stress and
pressure.  for at least this case, the pressure is "correct" i.e., compares well
w/the same problem run with a different code.  Attached is a matlab script for
visualization.  Or, a simple minmax on the files shows that Sxx Syy Szz are
about an order of magnitude smaller thatn Pressure.

(So far the shear stress cmpts look ok).