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

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

* 'lsfd--error' of https://github.com/masatake/util-linux:
  tests: (lsfd) add a case testing ERROR type appeared in TYPE column
  tests: (test_mkfds::mmap) new factory
  lsfd: add --_drop-prvilege option for testing purpose
  lsfd: add ERROR as a new type
  lsfd: (refactor) make the steps for new_file consistent
  lsfd: (refactor) add abst_class as super class of file_class
  lsfd: (refactor) simplify the step to make a file struct
  lsfd: (refactor) simplify the step to copy a file struct if the result of its stat is reusable
  lsfd: (refactor) flatten bit fields in struct file
  lsfd: fix typos of a function name