Re: Duplicate Workers entries in some EXPLAIN plans

I wrote:
> It's still really unclear to me how we could exercise any of
> this behavior meaningfully in a regression test. I thought
> for a little bit about using the TAP infrastructure instead
> of a traditional-style test, but it seems like that doesn't
> buy anything except for a bias towards ignoring details instead
> of overspecifying them. Which is not much of an improvement.

After further thought, I decided that about the best we can do
is suppress the "Workers" field in the regression test's expected
output. This still gives us code coverage of the relevant code,
and we can check that the output is valid JSON before we strip it,
so it's not a dead loss.

I rewrote the test script a bit to add some coverage of XML and YAML
output formats, since we had exactly none before, and pushed it.

regards, tom lane