Provide a way to allow get_resource and get_parent_resource to return errors

that might occur during the parsing of the URI and/or the lookup of the
resource in the repository.

Specifically: return a dav_error* and move the returned dav_resource* to an
"out" parameter of the hook function.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87852 13f79535-47bb-0310-9956-ffa450edef68