Drop the role we create, so regression tests pass even when run more
than once against the same cluster, a problem noted by Tom Lane and
Jeff Janes. Also, rename the temporary role so that it starts with
"regress_", to make it unlikely that we'll collide with an existing
role name while running "make installcheck", per further gripe from
Tom Lane.
which is broken in some weird way that I don't understand. I think it
may be exposing a bug in the new psql --- for one thing, I get different
results when I run psql by hand than the regress script gets. What
the heck???