libpq URI and regression testing

Hi,

When I committed Alex Shulgin's patch to add URI support to libpq, I
included the test harness as well.  However, due to it being in a
separate subdirectory that did not previously had tests, it's not being
run by buildfarm.

It's not considered in "make installcheck-world" either.

What's the preferred way to make it automatically tested as much as
possible?  I know the buildfarm does not run "installcheck-world", so if
we want it there, it'd need a bit more code on the client side.  I think
it would be wise to have it also run on installcheck-world.

Hmm.  Just had this thought: not all platform support the same socket
types.  Maybe we should have separated the .in file in three parts:
IPv4, IPv6, unix-domain socket.  That way each platform would only run
tests that pertain to it.  Right now there's a single "regress.in" file
that lists all the tests.

Opinions?

--
Álvaro Herrera <alvherre@alvh.no-ip.org>