resignal __alarm__ignore__ if caught in an unrelated eval; wrap DnsResolver select() in eval to avoid "(in cleanup) __alarm__ignore__" warnings; avoid "Use of uninitialized value" in AsyncLoop

git-svn-id: https://svn.apache.org/repos/asf/spamassassin/trunk@1447572 13f79535-47bb-0310-9956-ffa450edef68