Correct the information written by ExtendedAccessLogValve when a format token x-O(XXX) is used so that multiple values for a header XXX are separated by commas. Identified by Coverity Scan.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1622187 13f79535-47bb-0310-9956-ffa450edef68