[InterNetNews/inn] 56773b: Exit with status 0 when printing usage message

[Julien ÉLIE]

  Branch: refs/heads/main
  Home:   https://github.com/InterNetNews/inn
  Commit: 56773b1dbce5d87dd1b5ed276bf45cb974b10bff
      https://github.com/InterNetNews/inn/commit/56773b1dbce5d87dd1b5ed276bf45cb974b10bff
  Author: Julien ÉLIE <Julien-Elie at users.noreply.github.com>
  Date:   2023-01-26 (Thu, 26 Jan 2023)

  Changed paths:
    M contrib/pullart.c
    M contrib/tunefeed.in
    M control/controlbatch.in
    M frontends/cnfsheadconf.in
    M frontends/cnfsstat.in
    M frontends/ovdb_stat.c
    M scripts/innreport.in

  Log Message:
  -----------
  Exit with status 0 when printing usage message

Homogenize the exit status of INN programs when explicitly run with
a flag asking for printing their usage messages.  Status 0 should be
returned instead of 1.

Also, homogenize the format of the usage message.

close #254