suzerain: #3034 avoid stats loss on NaN

Fix plays a dodgy game with when dt_stats "sees" the
current_dt_.  Gets through regressions and behaves as
desired on a manual test case.

Adds "finite" modifier to driver output to avoid
confusion as to what the data means when a NaN is encountered.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@43518 0bd85f0b-c151-43b9-a1e9-27231104551f