Set currency template variable from contribution pages

When we load the PaymentForm the currency is set there and assigned to the template.

However, if the form doesn't load by default (ie because there is no payment processor selected by
default) the currency variable is not assigned to the template.

When the payment form is loaded by
      var dataUrl = '{crmURL p='civicrm/payment/form' h=0 q=formName=

CRM/Contribute/Form/ContributionBase.php

@@ -484,8 +484,13 @@ public function preProcess() {
     $this->_defaults = array();
 
     $this->_amount = $this->get('amount');
+    // Assigning this to the template means it will be passed through to the payment form.
+    // This can, for example, by used by payment processors using client side encryption
+    $this->assign('currency', $this->getCurrency());
 
     //CRM-6907
+    // these lines exist to support a non-default currenty on the form but are probably
+    // obsolete & meddling wth the defaultCurrency is not the right approach....
     $config = CRM_Core_Config::singleton();
     $config->defaultCurrency = CRM_Utils_Array::value('currency',
       $this->_values,

CRM/Core/Payment/ProcessorForm.php

@@ -72,8 +72,7 @@ public static function preProcess(&$form, $type = NULL, $mode = NULL) {
 
     $form->assign('suppressSubmitButton', $form->_paymentObject->isSuppressSubmitButtons());
 
-    $currency = $form->getCurrency();
-    $form->assign('currency', $currency);
+    $form->assign('currency', $form->getCurrency());
 
     // also set cancel subscription url
     if (!empty($form->_paymentProcessor['is_recur']) && !empty($form->_values['is_recur'])) {