Fix BN_gcd() to check return value when calling BN_one().

Add a check for the return of i2s_ASN1_INTEGER().

Fix X509v3_addr_add_range(), X509v3_addr_canonize(), and X509v3_addr_is_canonical() to return the correct result.

Fix memory leak in EC_GROUP_new_from_ecparameters().

Add and improve various checks.