Fix https://bz.apache.org/bugzilla/show_bug.cgi?id=58660

      With mapperContextRootRedirectEnabled ste to false, the redirect needs to be handled elsewhere.
- Ensure the Mapper does not add the '/'
- Handle the redirect in the DefaultServlet
- Add a redirect to FORM auth if auth is occurring at the context root else the login page could be submitted to the wrong web application

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1716882 13f79535-47bb-0310-9956-ffa450edef68