DNSBL Incremental Counter

Each time we receive an ip report, it should be counted as reported incrementally.
Since Mail2BL discards anything that is received again, it's important to add incremental function to the importer too.

In the future, this may have an effect on both PenaltyDB and the delisting tools, since high-volume-spamsites can be rated differently on delistings while low-volume-spamsites should be handled with shorter times.