Merge r1746207 from trunk:

mod_dav: Add support for childtags to dav_error.

Submitted by: minfrin
Reviewed by: minfrin, jim, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1756560 13f79535-47bb-0310-9956-ffa450edef68