suzerain: #3003 relax const-ness

I want to modify member data within these constraints after they
are established, so relatx the const-ness requirement.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@42845 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: #3003 progress on baseflow constraints

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@42846 0bd85f0b-c151-43b9-a1e9-27231104551f