suzerain: #3037 warn just once on profile errors

A compromise.  Multiple warnings in a simulation is rather annoying, but getting
some indication of a hiccup is good from a usability perspective.  A warning is
very important from a once-only postprocessing computation.  So just warn once
and add a TODO to do something smarter in this regard.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@44043 0bd85f0b-c151-43b9-a1e9-27231104551f