Add an alert for module developers that this subset (specifically,

only the recently added 2.4.17 Protocol API's) may still be in flux,
until the group has concensus on the API behavior.



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1718645 13f79535-47bb-0310-9956-ffa450edef68