Add --limit to limit latency under throttling
Under throttling, transactions are scheduled for execution at certain 
times. Transactions may be far behind schedule and the system may catch up 
with the load later. This option allows to change this behavior by 
skipping transactions which are too far behind schedule, and count those 
as skipped.
The idea is to help simulate a latency-constrained environment such as a 
database used by a web server.
-- 
Fabien.