An odd IPv6 application issue

[George Bonser]

> The end result is, with an operating system which uses bindv6only=1,
> you
> can only use IPv4 *or* IPv6, not both.
> 
> bindv6only=1 is the default on all BSD systems and at least recent
> versions
> of Debian.

Which is what I think I want.  If the destination is v6, open a v6 socket.  If the destination is v4, open a v4 socket.  Don't open a v6 socket that uses mapped v4 addressing (that's just silly, in my opinion).