[Patch] Pop3 statistics with dovecot not created

[aseques]

Recently I realized that no POP3 statistics were being generated in case you use dovecot.
Since most of the traffic is POP3 I just fixed that for my server.
Basically I tweaked some values from dovecot output to match the pattern that ispcp needs:

user=user@example.com top=0 retr=size

I know it won't be in next rc, but if someone could have a look at it, I'd be glad to add the patch to the documentation ...

Cheers