suzerain: move sum_acc_type into perfect.hpp

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@43675 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: use better accum pattern

Permits detecting usage mistakes

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@43676 0bd85f0b-c151-43b9-a1e9-27231104551f