pgbench: allow to exit immediately when any client is aborted

Hi,

I would like to propose to add an option to pgbench so that benchmark
can quit immediately when any client is aborted. Currently, when a
client is aborted due to some error, for example, network trouble, 
other clients continue their run until a certain number of transactions
specified -t is reached or the time specified by -T is expired. At the
end, the results are printed, but they are not useful, as the message
"Run was aborted; the above results are incomplete" shows.

For precise benchmark purpose, we would not want to wait to get such
incomplete results, rather we would like to know some trouble happened
to allow a quick retry. Therefore, it would be nice to add an option to
make pgbench exit instead of continuing run in other clients when any
client is aborted. I think adding the optional is better than  whole
behavioural change because some users that use pgbench just in order
to stress on backends for testing purpose rather than benchmark might
not want to stop pgbench even a client is aborted. 

Attached is the patch to add the option --exit-on-abort.
If this option is specified, when any client is aborted, pgbench
immediately quit by calling exit(2).

What do you think about it?

Regards,
Yugo Nagata
-- 
Yugo NAGATA <nagata@sraoss.co.jp>