incorrect docs for pgbench / skipped transactions

Hi,

while learning about format of the transaction log produced by pgbench,
I've noticed this sentence in the section describing format of the
per-transaction log:

The last field skipped_transactions reports the number of
transactions skipped because they were too far behind schedule.
It is only present when both options --rate and --latency-limit
are used.

Which is wrong, because this field is only added in the aggregated log,
not in the per-transaction one. So we should delete this.

It also does not explicitly explain that with --latency-limit the
latency column will contain "skipped" for transactions exceeding the
limit latency (it's only mentioned in the example output).

So I think we should apply the attached patch (and also backpatch it to
9.5, where the --latency-limit got introduced).

regards

--
Tomas Vondra http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services