Merge r1597349,1598107,1603915,1605827,1605829 from trunk:

mod_ssl: Fix tmp DH parameter leak, adjust selection to prefer
larger keys and support up to 8192-bit keys.

Submitted by: rpluem, jorton
Reviewed by: ylavic, kbrand


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1610014 13f79535-47bb-0310-9956-ffa450edef68