Finer grained fedmsg filtering

[labbott]

Currently, we get fedmsg notification for new reports at 10, 100, 1000 etc. This is useful for seeing that problems are approaching but many times these are reports of old problems that have been fixed. We don't really want reports on old kernels. It would be useful to have some notion of "This problem hit n reports AND the last report was on a recent kernel"