Merge r1684636 from trunk:

* mod_auth_digest: Use anonymous shm by default, fall back on name-based.

Submitted by: jkaluza
Reviewed by: jorton, ylavic, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1782175 13f79535-47bb-0310-9956-ffa450edef68