rec: replace data in the aggressive cache if it becomes available

rec: replace data in the aggressive cache if it becomes available

Currently, new data does not get recorded into the aggressive cache
if there's an existing entry that matches. Together with the fact
that in some cases pruning can be unfair (it scans the zones
always in the same order and stops clearing when it has reached the
goal) and/or not very active (when the recursor is lighlty loaded)
this has the consequence that old expired records can remain in
the cache that prevent new data to be recorded and used.