mod_ssl: Make the config parser complain if SSLRandomSeed specifies

the Entropy Gathering Daemon (EGD) as source while the underlying
SSL library does not support EGD (e.g. in case of LibreSSL).

Suggested and reviewed by: kbrand


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1675410 13f79535-47bb-0310-9956-ffa450edef68