Bug 6547: let Client.pm use the same logic as DnsResolver.pm in deciding which of the IO modules to use (IO::Socket::IP preferred to older IO::Socket::INET6, which in turn is preferred to IPv4-only IO::Socket::INET)

git-svn-id: https://svn.apache.org/repos/asf/spamassassin/trunk@1441536 13f79535-47bb-0310-9956-ffa450edef68