Pass order object to hook_commerce_paypal_wpp_request_alter()

I propose that we pass the order object to hook_commerce_paypal_wpp_request_alter(). This will make it easier to update the paypal request name-value pairs based on the state of the current order. While it is currently possible to pull the order number from the $nvp['CUSTOM'] string and load the order, it would be more reliable to have the order object passed in the drupal_render() call.

I'll use my current situation as an example. I'm using commerce_multicurrency to allow users to select from multiple currencies. In order to send the order totals to paypal in the user's selected currency, I've implemented hook_commerce_paypal_wpp_request_alter() in a small custom module to make this happen.

function commerce_multicurrency_paypal_wpp_commerce_paypal_wpp_request_alter(&$nvp, $order) {
  
  // The following 2 lines can be removed if the order object is passed as an argument
  //$order_number = intval(substr($nvp['CUSTOM'], 6));
  //$order = commerce_order_load_by_number($order_number);

  // get currency code from order
  $order_currency_code = $order->commerce_order_total['und'][0]['currency_code'];

  // update $nvp if
  //  order's currency code is different from PayPal currency code
  //  AND order's currency code is an available PayPal currency code
  if ($order_currency_code != $nvp['CURRENCYCODE'] && in_array($order_currency_code, array_keys(commerce_paypal_wpp_currencies()))) {
    $nvp['CURRENCYCODE'] = $order_currency_code;
    $nvp['AMT'] = round(commerce_currency_amount_to_decimal($order->commerce_order_total['und'][0]['amount']), 2);
  }
}