MFH: r369467

- Update to patchlevel 27 which changes how functions are exported.
  This should eliminate the recent vulnerabilities, but keep the
  requirement for --import-functions/IMPORTFUNCTIONS option for now.
- Loosen the --import-functions requirement so it is not needed when running
  an interactive shell. It is already disallowed for privileged/setuid mode.
- Show an error on stderr when an imported function is ignored.