example-config: Fix postmaster_address comment The default value was wrong.

lda, lmtp: postmaster_address = postmaster@%d works now.

example-config: Updated hostname setting's comments.

lib-lda: Added submission_host setting to send mails via SMTP instead of sendmail.

example-config: sendmail_path defaults to /usr/sbin/sendmail, not /usr/lib/sendmail

Added lda_original_recipient_header setting. Removed non-standard use of Envelope-To: header.

Fixing my english: s/non-?existing/nonexistent/

example-config: Added nn- prefix to *.conf files so the sort ordering makes more sense. This is especially important to get mail_plugins = $mail_plugins example working in protocol sections. --HG-- branch : HEAD