- autoflush for stderr enabled

- in check_file_fixities() using Path::Tiny::openr()_raw instead open_r() to avoid extra binmode() call
- extracted common stuff from while-loop in stage2() to stage2_for_ie(),
  this could reduce the memory footprint because reduced scope
- in stage2() instead seek we close and reopen fh now
HINT: no real reason for "out of memory"-problem found