mod_ssl: Check for RAND_egd() at configure time and only use it if present.
Fixes the build with LibreSSL which does not provide this function.

Submitted by: Bernard Spil <pil.oss gmail com>, stsp
Committed by: stsp


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


Follow up to r1674542 and r1675410: CHANGES entry.
Submitted by: stsp, ylavic
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1679199 13f79535-47bb-0310-9956-ffa450edef68