* track searches more carefully

* detect situations where we may be inadvertantly flooding the netDb
and log them as CRIT with a stacktrace, as well as publish the count
of those events in the netDb
* detect potential netDb DoS situations by checking to see if we have
received more than 20 netDb lookups in 10 seconds, and if so,
probabalistically drop subsequent netDb messages (P=1-(10/numReceived)).
This is also published in the netDb.