Use the latest point release of Postgres for testing

Signed-off-by: Daniel Farina <daniel@fdr.io>
Make log periodic flushing more aggressive

This was feedback that the current system had too much of a
perceptible delay.  It will probably lead to dropping a lot more logs
and a lot more burden on logplex, though.

A better system would probably involve some adaptivity, such a token
bucket that gives good response time for less-heavily used databases
with infrequent log traffic while taking advantage of more batching
for databases with a lot more log traffic.

Signed-off-by: Daniel Farina <daniel@fdr.io>