suzerain: #2979 ACCUMULATE not clobber

I'd miscoded Step 4 from copy'n'paste of the transpose.  This
at least shows reasonable behavior on taking miniscule steps
from a laminar base flow.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@43848 0bd85f0b-c151-43b9-a1e9-27231104551f