An incompatibility has always existed between the format used for RSA

signatures and MDC2 using EVP or RSA_sign. This has become more apparent
when the dgst utility in OpenSSL 1.0.0 and later switched to using the
EVP_DigestSign functions which call RSA_sign.

This means that the signature format OpenSSL 1.0.0 and later used with
dgst -sign and MDC2 is incompatible with previous versions.

Add detection in RSA_verify so either format works.

Note: MDC2 is disabled by default in OpenSSL and very rarely used in practice.