OpenSSL: don't use direct access to the internal of X509_STORE

OpenSSL: don't use direct access to the internal of X509_STORE

OpenSSL 1.1 does not allow us to directly access the internal of
any data type, including X509_STORE. We have to use the defined functions
to do so.

Compatibility with OpenSSL 1.0 is kept by defining the corresponding
functions when they are not found in the library.

Signed-off-by: Emmanuel Deloget <logout@free.fr>
Acked-by: Steffan Karger <steffan.karger@fox-it.com>
Message-Id: <8e6d66e3a9a40abb3d7c99c48ba59bad1037d0ef.1487368114.git.logout@free.fr>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg14076.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>
(cherry picked from commit f05665df4150c6a345eec5432a02fd799bea0f2c)