Add Auto-Submitted header field in outgoing mails

[Julien-Elie]

Our programs should implement RFC 3834 and accurately add an Auto-Submitted: auto-generated/auto-replied header field.

This could help to avoid unnecessary vacation replies and support automatic e-mail filtering.

Programs sending mails:

• Daily Usenet reports (news.daily);
• newgroup/rmgroup/checkgroups reports (controlchan);
• top1000 reports (sendinpaths);
• failure or warning reports from various programs (mailpost, expirerm, rc.news, innwatch, writelog);
• our internal wrapper to sendmail or like (innmail, with a new -a option based on mail(1) to specify an additional header field);
• gatewaying (news2mail);
• forwarding to a moderator (nnrpd).