Merge remote-tracking branch 'refs/remotes/origin/master'

* refs/remotes/origin/master:
  locking.c, locking.1: Make the protocol safe if the lockfile is (re)moved.
  locking.c: Refactor the main locking flow.
  locking.c: Use shell convention to report child killed by a signal.
  locking.c: Rename exit status variable to `rc'.
  locking.c: Compress vertically.  Remove pointless `$Id' comment.