Input on "most correct" way to set IS_INTERACTIVE for Postfix ports

[rflynn at acsalaska.net]

> mail/postfix and its derivatives are interactive when ALL of the
> following conditions are true:
>
>  - PACKAGE_BUILDING is undefined
>  - /etc/mail/mailer.conf exists
>  - /etc/mail/mailer.conf contains a line beginning with 'purgestat'
   - POSTFIX_DEFAULT_MTA is unset

And that one seems the cleanest to use. Especially if you fix the script
to preserve \$FreeBSD.*\$$.

-- Mel