ioping: switch stdout into line-buffered mode

By default stdout is line-buffered only for terminals.
Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Link: http://code.google.com/p/ioping/issues/detail?id=17

ioping.c

@@ -842,6 +842,8 @@ int main (int argc, char **argv)
 	double part_sum, part_sum2, part_mdev, part_avg;
 	long long time_now, time_next, period_deadline;
 
+	setvbuf(stdout, NULL, _IOLBF, 0);
+
 	parse_options(argc, argv);
 
 	interval_ts.tv_sec = interval / 1000000;