2020Q2 specific mail/mailman minimal security fix

Backporting 2.1.31 needs more consideration and more than just MFH r534101,
so forgo that and for the nonce, plug this information leak quickly with the
one-line fix by upstream, and hack additional translations to match into the
.po files with REINPLACE_CMD.

Approved by: ports-secteam@ (blanket, trivial security fix)
Security: 88760f4d-8ef7-11ea-a66d-4b2ef158be83