Ensure that the result of calling HttpServletRequest.getContextPath() is neither decoded nor normalized as required by the Servlet specification.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1644975 13f79535-47bb-0310-9956-ffa450edef68
Follow on to r1642702
Only currently running contexts should be returned.
Handle the case where the mapper returns an unwanted non-exact match.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1645015 13f79535-47bb-0310-9956-ffa450edef68