Merge r1523239 from trunk:

mod_auth_digest: Be more specific when the realm mismatches because the
realm has not been specified.

Submitted by: minfrin
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1524172 13f79535-47bb-0310-9956-ffa450edef68