Patch for testing query modes on pgbench

Here is a updated patch to add query modes into pgbench in order to
measure performance of simple protocol, extended protocol and
prepared statements with it.

[PATCHES] Patch for testing query modes on pgbench
http://momjian.us/mhonarc/patches/msg00335.html

A new runtime option (-M) is added:
-M querymode
Choose the query mode from the follows. default is simple.
- simple: using simple query protocol.
- extended: using extended protocol.
- prepared: using extended protocol with prepared statements.

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Extended protocol is slower than simple protocol. I think it is a problem
because we have to use the protocol (and cannot use prepared statements)
in some situations, such as connectiong with JDBC to partitioned tables.

$ pgbench -S -n -c5 -t10000 -M simple
tps = 3567.351598 (excluding connections establishing)
$ pgbench -S -n -c5 -t10000 -M extended
tps = 2877.697842 (excluding connections establishing)
$ pgbench -S -n -c5 -t10000 -M prepared
tps = 4532.680627 (excluding connections establishing)

Regards,
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ITAGAKI Takahiro
NTT Open Source Software Center