mod_dav: Add dav_begin_multistatus, dav_send_one_response,

dav_finish_multistatus, dav_send_multistatus, dav_handle_err, 
dav_failed_proppatch, dav_success_proppatch to mod_dav.h.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1748047 13f79535-47bb-0310-9956-ffa450edef68