cmd_receive: treat 'quit' or other non- yes/no answers as "no"
cmd_receive: treat 'quit' or other non- yes/no answers as "no"

So "yes" or "Yes" or "y" or "Y" or anything else that starts with y/Y means
yes, and a bare newline means yes, but anything else means no.

warner/magic-wormhole,warner/magic-wormhole,warner/magic-wormhole,warner/magic-wormhole