Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=50771

      Ensure HttpServletRequest#getAuthType() returns the name of the authentication scheme 
if request has already been authenticated. (kfujino)

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc5.5.x/trunk@1158238 13f79535-47bb-0310-9956-ffa450edef68