Fix https://bz.apache.org/bugzilla/show_bug.cgi?id=61201

      Ensure that the SCRIPT_NAME environment variable for CGI executables is populated in a consistent way regardless of how the CGI servlet is mapped to a request.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1799368 13f79535-47bb-0310-9956-ffa450edef68