Merge branch 'vipw-shortwrite' of https://github.com/DankRank/util-linux

Merge branch 'vipw-shortwrite' of https://github.com/DankRank/util-linux

* 'vipw-shortwrite' of https://github.com/DankRank/util-linux:
  ul_copy_file: make defines for return values
  read_all: return 0 when EOF occurs after 0 bytes
  ul_copy_file: add test program
  ul_copy_file: handle EAGAIN and EINTR
  ul_copy_file: use all_read/all_write
  ul_copy_file: use BUFSSIZ for buffer size
  nologin: use ul_copy_file
  login: use ul_copy_file
  configure.ac: check for sendfile
  ul_copy_file: use sendfile
  vipw: move copyfile to the lib
  vipw: fix short write handling in copyfile