suzerain: #3022 Ma,gamma pre adjust_scenario

Prior to this commit, I had --cevdstag processing mutating
scenario->gamma and scenario->Ma after the temperature-preserving
adjust_scenario call.  This caused negative total energy and
the advance NaNed out.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@43350 0bd85f0b-c151-43b9-a1e9-27231104551f
suzerain: #3022 #3020 T_e realizability

Incorporate basic material on how setting T_e can lead
to a non-realizable flow due to E <= 0.

git-svn-id: https://svn.ices.utexas.edu/repos/pecos/suzerain/trunk@43351 0bd85f0b-c151-43b9-a1e9-27231104551f