Support for OpenSSL 1.1.0:

- BIO was made opaque after OpenSSL 1.1.0pre4.

Partial backport of r1737657 from trunk.

Also patrially backported to reduce code drift:
add some log messages and AP_DEBUG_ASSERTs
for functions that should never be called

Partial backport of r1519264 from trunk.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x-openssl-1.1.0-compat@1755861 13f79535-47bb-0310-9956-ffa450edef68