Consolidated logic for choosing number of thread-MPI ranks
Noted TODO to handle issue that was always present, but is now
easy to see needs handling.
Added explicit fatal error for a case that a comment claimed was
handled later, but for which I could not find handling.
Removed some logic for nthreads_tot == 1 that was redundant with
that in get_nthreads_mpi and check_and_update_hw_opt_3.
Added explicit checks for -ntmpi and -ntomp greater than -nt,
replacing an old check that gave an incorrect message, and was only
used when -nt selected 1 total threads.
Change-Id: I6b6634ac4dd726a784a626624de4405a4ddb07f0