Remove pgbench constraint that the number of clients must be a multiple of
the number of threads, by sharing clients among threads as evenly as
possible.
Rational: allows to test the database load with any number of client
without unrelated constraint. The current setting means for instance that
testing with a prime number of clients always uses one thread, whereas
other number of clients can use a different number of threads. This
constraint does not make much sense.
--
Fabien.
