Support for OpenSSL 1.1.0:

- 1.1.0-pre3 was relesed
  - remove pre2 comments which no longer apply
  - one more struct has been made opaque, use
    accessor function instead

Backport of r1731012 from trunk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x-openssl-1.1.0-compat@1755843 13f79535-47bb-0310-9956-ffa450edef68