Correctly merge r1836287, backported in 2.4.x in r1836288.

(unless I missed something, the function is also called 'ap_directory_walk' in 2.4.x)

This is only a comment update.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1843284 13f79535-47bb-0310-9956-ffa450edef68