mod_dav: Note an API issue with the dav_hooks_repository.deliver(),

dav_hooks_vsn.deliver_report() and dav_hooks_vsn.merge() hook
definitions.

* modules/dav/main/mod_dav.h
  (dav_hooks_repository.deliver, dav_hooks_vsn.deliver_report,
   dav_hooks_vsn.merge): Add notes about the API issue.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1764043 13f79535-47bb-0310-9956-ffa450edef68