Document that the certificate passed to SSL_CTX_add_extra_chain_cert()
should not be freed by the application.
PR#3409
(cherry picked from commit 0535c2d67ca2d684087ef90be35d5fb207aab227)
Preliminary documentation for chain and verify stores and certificate chain
setting functions.
(cherry picked from commit eeb15452a053c14305210522be0e7313cb763bac)