Added support for postfix smtpd_smtp_proxy aka pre-queue filter

[csware]

Without this fix all "back-"connects of the smtp_proxy are counted as received and also NOQUEUE-lines which signals that the proxy will be asked are also counted as received.

[forkedjensh]

This one's a bit old, but:
I second the intention of this pull request, because mailgraph will count received mails twice in proxy filter mode.

Although there seems to be an error: In my opinion proxy-accept must not be counted. It's already there because of the first if clause. Both lines are matched by receiving one mail and counted with this change:

# first if clause
Aug  2 01:00:14 host postfix/smtpd[64923]: 5DF91100568: client=localhost[127.0.0.1], orig_client=client.private[XXX.XXX.XXX.XXX] 
# proxy-accept if clause
Aug  2 01:00:14 host postfix/smtpd[57674]: proxy-accept: END-OF-MESSAGE: 250 2.0.0 from MTA(smtp:[127.0.0.1]:10025): 250 2.0.0 Ok: queued as 5DF91100568; from=<sender@client.private> to=<recipient@target.private> proto=ESMTP helo=<client.private>

I have no possibility to test this patch with postfix in content filter mode, but the regexps look really non intrusive.

[schweikert]

I am not using mailgraph since a long time... Anybody wants to take over maintenanceship? The starting point would be to create a fork and integrate all the pending (and senseful) patches.