backport r1379311: Add a notion that, for a skip flag to be used, the rewrite...

backport r1379311: Add a notion that, for a skip flag to be used, the rewrite rule has to first match (as per comment #211 on site)

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1379703 13f79535-47bb-0310-9956-ffa450edef68