The Debian-provided stunnel4 package drags in perl-modules, which we wanted
to avoid installing, and it only needs it for trivial support-script reasons,
so we compiled our own instead.

The only files installed are /usr/local/bin/stunnel,
/usr/local/lib/stunnel/libstunnel.so and /etc/stunnel/stunnel.pem (a
self-signed certificate for localhost).