Use PREPARE/EXECUTE statements for applying DML in follow mode. (#420)

* Introduce Bob Jenkins lookup3 hash function.

* Use PREPARE/EXECUTE statements for applying DML in follow mode.

When replaying INSERT/UPDATE/DELETE statements, switch to using PREPARE and
EXECUTE at the protocol level (using the libpq functions PQprepare and
PQexecPrepared). When a statement has already been prepared previously in
our session, we then only send the EXECUTE statement.

This shoud provide nice performance improvements.

* Fix ci/banned.h.sh.

Avoid using sscand(), use strtoull with a base 16 instead. In passing
clean-up some extra logging.

* Code review and refactoring.

* Suppress compilation warnings from Jenkins lookup3.c code.