Fix assorted portability issues in new pgbench TAP tests.

Fix assorted portability issues in new pgbench TAP tests.

* Our own version of getopt_long doesn't support abbreviation of
long options.

* It doesn't do automatic rearrangement of non-option arguments to the end,
either.

* Test was way too optimistic about the platform independence of
NaN and Infinity outputs.  I rather imagine we might have to lose
those tests altogether, but for the moment just allow case variation
and fully spelled out Infinity.

Per buildfarm.