register_socket() missed a variable declaration if neither
HAVE_SYS_EPOLL_H nor HAVE_SYS_EVENT_H was defined.

While we're fixing that, adjust the tests to check pg_config.h for one
of the multiplexer implementations, rather than assuming that Windows is
the only platform without support. (Christoph reported this on
hurd-amd64, an experimental Debian.)

Reported-by: Christoph Berg <myon@debian.org>
Discussion: https://postgr.es/m/Z-sPFl27Y0ZC-VBl%40msg.df7cb.de

The connect_timeout=1 setting for the --hang-forever test was kept in
place for later tests, causing unexpected timeouts on slower buildfarm
animals. Remove it.

Reported-by: Andres Freund <andres@anarazel.de>

Requires Python 3. On the first run of `make installcheck` or `meson
test` the dependencies will be installed into a local virtualenv for
you. See the README for more details.

Cirrus has been updated to build OAuth support on Debian and FreeBSD.

The suite contains a --temp-instance option, analogous to pg_regress's
option of the same name, which allows an ephemeral server to be spun up
during a test run.

TODOs:
- The --tap-stream option to pytest-tap is slightly broken during test
  failures (it suppresses error information), which impedes debugging.
- pyca/cryptography is pinned at an old version. Since we use it for
  testing and not security, this isn't a critical problem yet, but it's
  not ideal. Newer versions require a Rust compiler to build, and while
  many platforms have precompiled wheels, some (FreeBSD) do not. Even
  with the Rust pieces bypassed, compilation on FreeBSD takes a while.
- The with_oauth test skip logic should probably be integrated into the
  Makefile side as well...
- See if 32-bit tests can be enabled with a 32-bit Python.