getinfo: CURLINFO_TLS_SSL_PTR supersedes CURLINFO_TLS_SESSION

The two options are almost the same, except in the case of OpenSSL:

CURLINFO_TLS_SESSION OpenSSL session internals is SSL_CTX *.

CURLINFO_TLS_SSL_PTR OpenSSL session internals is SSL *.

For backwards compatibility we couldn't modify CURLINFO_TLS_SESSION to
return an SSL pointer for OpenSSL.

Also, add support for the 'internals' member to point to SSL object for
the other backends axTLS, PolarSSL, Secure Channel, Secure Transport and
wolfSSL.

Bug: https://github.com/curl/curl/issues/234


Reported-by:  <dkjjr89@users.noreply.github.com>

Bug: https://curl.haxx.se/mail/lib-2015-09/0127.html
Reported-by: Michael König