Patch for testing query modes on pgbench

Here is a patch for testing query modes on pgbench. It is discussed on
http://archives.postgresql.org/pgsql-hackers/2007-10/msg00755.php

I think this is useful to measure performance of protocols and
prepared statements. I hope the extended protocol will be improved
as fast as the simple protocol. It is 10-20% slower now.
(for 8.4 item)

The querymode option is added:
    -M querymode
        Choose the query mode from the follows:
            simple: using simple query protocol.
            extended: using extended protocol.
            prepared: using extended protocol with prepared statements.
        default is simple.

Usage:
$ pgbench -M [simple|extended|prepared]

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center