related to Bug 6841: testing for PF_INET and PF_INET6 availability in spamd allows automatic choice of default protocol families for listen sockets (like on an IPv6-only host); documentation details; more informative debugging

git-svn-id: https://svn.apache.org/repos/asf/spamassassin/trunk@1451230 13f79535-47bb-0310-9956-ffa450edef68