[PATCH] add --progress option to pgbench

Please find attached a small patch submission, for reference to the next 
commit fest.

Each thread reports its progress about every the number of seconds 
specified with the option. May be particularly useful for long running 
pgbench invocations, which should always be the case.
 shell> ./pgbench -T 16 --progress 5 -c 4 -j 2 test starting vacuum...end. thread 0 running at 53.194457 tps after 5.0
sthread 1 running at 59.792203 tps after 5.0 s [ bzzzz... ] thread 0 running at 56.050592 tps after 10.0 s thread 1
runningat 54.075444 tps after 10.1 s [ bzzzz... ] thread 0 running at 49.746026 tps after 15.0 s thread 1 running at
48.560258tps after 15.1 s [ bzzzz... ] transaction type: TPC-B (sort of) scaling factor: 1 query mode: simple number of
clients:4 number of threads: 2 duration: 16 s number of transactions actually processed: 1725 tps = 107.034958
(includingconnections establishing) tps = 107.094691 (excluding connections establishing)
 


-- 
Fabien.