BUG/MINOR: ssl: fix build with openssl < 1.1.0

8c1cddef ("MINOR: ssl: new functions duplicate and free a ckch_store")
use some OpenSSL refcount functions that were introduced in OpenSSL
1.0.2 and OpenSSL 1.1.0.

Fix the problem by introducing them in openssl-compat.h.

Fix #336.
1 file changed