CRM-13675 sort pdfs by sort name

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* CRM-13675: Membership activities are unsorted - which is confusing on pdf letters
  http://issues.civicrm.org/jira/browse/CRM-13675

CRM/Member/Form/Task/PDFLetterCommon.php

@@ -41,7 +41,8 @@ class CRM_Member_Form_Task_PDFLetterCommon extends CRM_Contact_Form_Task_PDFLett
   static function generateHTML($membershipIDs, $returnProperties, $skipOnHold, $skipDeceased, $messageToken, $html_message, $categories) {
     $memberships = CRM_Utils_Token::getMembershipTokenDetails($membershipIDs);
 
-    foreach ($memberships as $membershipID => $membership) {
+    foreach ($membershipIDs as $membershipID) {
+      $membership = $memberships[$membershipID];
       // get contact information
       $contactId = $membership['contact_id'];
       $params = array('contact_id' => $contactId);