losses. The advatage of doing it here is that we don't need to
re-create all of the checks a real TCP stack has to do - we just look
at what it decided. The downside, though, is that we don't find out
about loss until the retransmit happens, which could be a little while
later.

Also add checks for duplicate and old acks.

Convert to using Jon's new logging flags for low and medium detail
logging information.