suzerain: #3111 use amax/yamax

I was picking up small magnitude (but ever so slightly positive) uv
fluctuations.  This is sane because uv is negative.  I want to
report large negative values but maintain their sign.  Hence,
this change.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45242 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: use unordered header_shown

Membership checks are all I want here, so stop using an
O(N ln N) operation for it.  Though, admittedly, the
number of tracked instances is low.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@45243 0bd85f0b-c151-43b9-a1e9-27231104551f