Add a bit more debug when requests fail

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/net/trunk@1648228 13f79535-47bb-0310-9956-ffa450edef68
Allow overwrite of mbox file

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/net/trunk@1648244 13f79535-47bb-0310-9956-ffa450edef68