with `pw lock', so that it's impossible to log into a locked account
using an alternative authentication mechanism, such as an ssh key.
This change affects only accounts locked with pw(8), i.e., having a
`*LOCKED*' prefix in their password hash field, so people still can
use a different pattern to disable password authentication only.
Mention all account management criteria in the manpage.
Approved by: maintainer (timeout)
PR: bin/71147
MFC after: 1 month
cf21ead53b