LOG4NET-205 fixed LoggingEvent to put the UserNameProperty and the IdentityProperty into the composite properties dictionary

This way the PropertyFilter can look up and filter by UserName and Identity.

git-svn-id: https://svn.apache.org/repos/asf/logging/log4net/trunk@1511303 13f79535-47bb-0310-9956-ffa450edef68