upstream: when prompting the user to accept a new hostkey, display

upstream: when prompting the user to accept a new hostkey, display

any other host names/addresses already associated with the key. E.g.

> The authenticity of host 'test (10.0.0.1)' can't be established.
> ECDSA key fingerprint is SHA256:milU4MODXm8iJQI18wlsbPG7Yup+34fuNNmV08qDnax.
> This host key is known by the following other names/addresses:
>     ~/.ssh/known_hosts:1: host.example.org,10.0.0.1
>     ~/.ssh/known_hosts:2: [hashed name]
>     ~/.ssh/known_hosts:3: [hashed name]
>     ~/.ssh/known_hosts:4: host
>     ~/.ssh/known_hosts:5: [host]:2222
> Are you sure you want to continue connecting (yes/no/[fingerprint])?

feedback and ok markus@

OpenBSD-Commit-ID: f6f58a77b49f1368b5883b3a1f776447cfcc7ef4