suzerain: improve tke plot

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45554 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: permit positive, negative thresh

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45555 0bd85f0b-c151-43b9-a1e9-27231104551f