suzerain: permit fixing x axis

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45484 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: add optional channel averaging

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45485 0bd85f0b-c151-43b9-a1e9-27231104551f