In the decade (!) since this corpus was last updated, the keyserver
network is essentially dead, and I have migrated gpg keys. Bump the
version number as a clean way of switching signatures. Also update the
instructions to suggest using "--locate-external-key" to download the
public key. By default this uses WKD, which is now supported for my
UID.
This is not near as fancy as as the unit tests, on the theory that
the code should typically be crashing when performance tuning.
Nonetheless, there is plenty of room for improvement. Several more of
the pieces of the test infrastructure (e.g. the option parsing) could
be factored out into test/test-lib-common.sh
