curl: SSL options ISSUERCERT, EC_CURVES and CRLFILE silently ignored by non-OpenSSL backends

Summary: The SSL options ISSUERCERT, ECCURVES and CRLFILE are silently ignored for e.g. the mbedTLS backend, which allows MITM attacks for the ISSUERCERT and CRLFILE bug, and can reduce the security and compliance by ignoring the specified curve for the ECCURVES bug. Affected version Tested with...