Merge r591499, r593919 from trunk:

spurious 401s with message "DN has not been defined" when cache expiration happens in another thread

PR 43786



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@595675 13f79535-47bb-0310-9956-ffa450edef68