changed Protocols default to http/1.1 only, updated documentation, changed...

changed Protocols default to http/1.1 only, updated documentation, changed ap_select_protocol() to return NULL when no protocol could be agreed upon

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1701005 13f79535-47bb-0310-9956-ffa450edef68