Improve regression test coverage of regress.c.

Improve regression test coverage of regress.c.

It's a bit silly to have test functions that aren't tested, so test
them.

In passing, rename int44in/int44out to city_budget_in/_out so that they
match how the regression tests use them.  Also, fix city_budget_out
so that it emits the format city_budget_in expects to read; otherwise
we'd have dump/reload failures when testing pg_dump against the
regression database.  (We avoided that in the past only because no
data of type city_budget was actually stored anywhere.)

Discussion: https://postgr.es/m/29322.1519701006@sss.pgh.pa.us