+ \param match_schema matched schema (if conversion was successful)
+ \param match_syntax matced syntax OID if conversion was successful)
+ \param rc record conversion reference (if conversion was successful)
+ \param backend_schema backend scchema (if conversion was successful)
+ \param backend_syntax backend syntax (if conversion was successful)
+ \retval 0 success, schema and syntax matches
+ \retval -1 failure, use yaz_retrieval_get_error() for reason
+ \retval 1 schema does not match
+ \retval 2 syntax does not match
+ \retval 3 both match but not together