Improve regression test coverage for psql output formats.

As penance for the "\pset format latex" silliness, add some regression
test coverage for the off-the-beaten-path output formats, which formerly
had exactly no coverage, except for some poorly-thought-out (unreadable,
repetitive, and incomplete) tests for asciidoc format.

I make no claims for the behavior exposed here actually being correct;
these test cases are just designed to ensure full code coverage in
fe_utils/print.c.  This brings the line coverage for that file up
from ~60% to ~93%.

Author: tglsfdc