Merge branch 'lsfd--add-error-c' of https://github.com/masatake/util-linux

* 'lsfd--add-error-c' of https://github.com/masatake/util-linux:
  lsfd: (refactor) move the error object related code to a new file
  lsfd: (refactor) remove redundant is_error member from struct file
  lsfd: (refactor) add a helper function making error file objects
  lsfd: remove __unused__ attr from parameters used actually
  lsfd: (cosmetic) adjust white spaces in column definitions