Make CT_POLICY_EVAL_CTX_set1_{cert,issuer} into boolean functions

They may fail if they cannot increment the reference count of the
certificate they are storing a pointer for. They should return 0 if this
occurs.

Reviewed-by: Emilia Käsper <emilia@openssl.org>
Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1408)