The error message added in 379695d3cc70 referred to the public key being
too long. This is confusing as it is in fact the session key included
in a PGP message which is too long. This is harmless, but let's be
precise about what is wrong.
Per offline report.
Reported-by: Zsolt Parragi <zsolt.parragi@percona.com>
Backpatch-through: 14