pgsql: Enhance pgbench -l option to add timestamp.

Log Message:
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Enhance pgbench -l option to add timestamp. Patch contributed by Greg
Smith. Along with Japanese doc updation by Tasuo Ishii.

This patch changes the way pgbench outputs its latency log files so that
every transaction gets a timestamp and notes which transaction type was
executed. It's a one-line change that just dumps some additional
information that was already sitting in that area of code. I also made a
couple of documentation corrections and clarifications on some of the more
confusing features of pgbench.

It's straightforward to parse log files in this format to analyze what
happened during the test at a higher level than was possible with the
original format. You can find some rough sample code to convert this
latency format into CVS files and then into graphs at
http://www.westnet.com/~gsmith/content/postgresql/pgbench.htm which I'll
be expanding on once I get all my little patches sent in here.

Modified Files:
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pgsql/contrib/pgbench:
README.pgbench (r1.16 -> r1.17)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgbench/README.pgbench.diff?r1=1.16&r2=1.17)
README.pgbench_jis (r1.17 -> r1.18)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgbench/README.pgbench_jis.diff?r1=1.17&r2=1.18)
pgbench.c (r1.63 -> r1.64)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/contrib/pgbench/pgbench.c.diff?r1=1.63&r2=1.64)