BUG: Nastran reading of free format truncates last field (fixes #3189)

- the old logic relied on the presence/absence of a comma to decide
  whether to parse as fixed or free format. This logic is faulty when
  handling the final (trailing) entry and will generally lead to the
  last field being truncated when read in.
  Now the caller decides on fixed vs free.

FIX: inconsistent Nastran surface output format

- use FREE format by default. Previously had an odd mix of SHORT
  format when created without options and LONG format (as default)
  when created with format options.