IPv6 support

IPv6 support

This patch, apparently, came from the freebsd syslogd.
The patch was subsequently lost although the old Fedora RPM can still
be found.

I took that patch, the current freebsd sources and a dash of salt to
produce a new patch which I have attached.

The patch does two things: it will arrange for syslogd to listen on an
IPv6 socket in addition to the IPv4 socket and it uses getaddrinfo()
and getnameinfo() rather than gethostby[name|addr] and getservbyname.
It would be possible to use a single socket that accepts both IPv6 and
IPv4 datagrams, but this would mean that numeric IPv4 addresses would
be prefixed with ::ffff and this could cause some confusion -- and I'm
also not sure that everything that sysklogd runs on has a dual stack
like that.

I've also introduced the -4, -6 and -A with the same meanings that the
freebsd and rsyslog variants do.