Updated backport proposal with the latest discussion on dev@

about Last-Modified header handling.
I removed jchampion's vote since it was related to a completely
different solution.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1757982 13f79535-47bb-0310-9956-ffa450edef68