- skip loading of fields with -no-internal, -no-boundary

- suppress reporting fields with -no-internal, -no-boundary

- cache loaded volume field for reuse with point interpolation.
  Trade off some memory overhead against reading twice.

  NOTE: this issue will not be evident with foamToEnsight since there
  it only handles cell data *or* point data (not both), so a field is
  only ever loaded/processed once.