Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56501
HttpServletRequest.getContextPath() should return the undecoded context path used by the user agent.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1593621 13f79535-47bb-0310-9956-ffa450edef68