Enforce OpenSSL 0.9.7 or later at compile time (#error out otherwise).

Remove some more unneeded defines from ssl_private.h.

At runtime, warn when mod_ssl is started with an OpenSSL version
older than the one it was originally compiled against.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1157575 13f79535-47bb-0310-9956-ffa450edef68