Merge r1563420 from trunk:

enable auto curve selection for ephemeral ECDH keys
when compiled against OpenSSL 1.0.2 or later

Submitted by: kbrand
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1569005 13f79535-47bb-0310-9956-ffa450edef68