pg_upgrade automatic testing

Seeing that 9.1-to-9.1 pg_upgrade has apparently been broken for months,
it would probably be good to have some kind of automatic testing for it.
Attached is something I hacked together that at least exposes the
current problems, easily available by typing "make check" and waiting.
It does not yet fully implement the full testing procedure in the
TESTING file, in particular the diffing of the dumps (well, because you
can't get there yet).

Is that something that people are interested in refining?

(I think it would even be possible under this setup to create special
regression test cases that are only run under the pg_upgrade test run,
to exercise particularly tricky upgrade cases.)