- Use precompiler conditionals in to_wire_mode() and from_write_mode()

- Use precompiler conditionals in to_wire_mode() and from_write_mode()
  to get rid of code that is not needed on the current system.
- Silence a code-checker warning in send_file_entry().
- Silence a code-checker warning in make_file().
- Fixed a bug in f_name_cmp() that could compare an empty filename
  incorrectly (which might only happen if we transformed a dot-dir
  into an empty name).  (Thanks, code checker!)