message: Replace panic for plain unreachable
diff: @@ -199,7 +199,7 @@ impl Api for ExternalApi {
  match result {
  1 => Ok(true),
  0 => Ok(false),
  - x => panic!(format!("unexpected secp256k1_verify return value: {}", x)),
  + _ => unreachable!(),
  }
  }
  