message: return the cbor encoded TxAux
diff: @@ -523,14 +523,20 @@ struct WalletSpendInput {
  #[derive(Serialize, Deserialize, PartialEq, Debug)]
  struct WalletSpendOutput {
  wallet: Wallet,
  - txaux: tx::TxAux
  + txaux: Vec<u8>
  }
  #[no_mangle]
  pub extern "C" fn xwallet_spend(input_ptr: *const c_uchar, input_sz: usize, output_ptr: *mut c_uchar) -> i32 {
  let mut input : WalletSpendInput = input_json!(output_ptr, input_ptr, input_sz);
  let txaux = jrpc_try!(output_ptr, input.wallet.new_transaction(&input.inputs, &input.outputs, &input.fee_addr));
  - jrpc_ok!(output_ptr, WalletSpendOutput { wallet: input.wallet, txaux: txaux })
  + jrpc_ok!(
  + output_ptr,
  + WalletSpendOutput {
  + wallet: input.wallet,
  + txaux: jrpc_try!(output_ptr, cbor::encode_to_cbor(&txaux))
  + }
  + )
  }
  #[derive(Serialize, Deserialize, PartialEq, Debug, Clone)]
  