PR59039 Digest not working with ap_expr based AuthName

Stop caching the configured realm during config processing and always
call ap_auth_name(r) to determine (=evaluate potential expression)
the configured realm



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1731662 13f79535-47bb-0310-9956-ffa450edef68