Ticket thread supports specifying `thread-type`

This allows the email system to detect something like a bounce mail and
specify that the associated message should be an internal note.

include/class.thread.php

@@ -575,6 +575,7 @@ Class ThreadEntry {
             'ip' =>     '',
             'reply_to' => $this,
         );
+        $errors = array();
 
         if (isset($mailinfo['attachments']))
             $vars['attachments'] = $mailinfo['attachments'];
@@ -591,7 +592,6 @@ Class ThreadEntry {
         elseif ($staff_id = Staff::getIdByEmail($mailinfo['email'])) {
             $vars['staffId'] = $staff_id;
             $poster = Staff::lookup($staff_id);
-            $errors = array();
             $vars['note'] = $body;
             return $ticket->postNote($vars, $errors, $poster);
         }
@@ -599,6 +599,15 @@ Class ThreadEntry {
             // Don't process the email -- it came FROM this system
             return true;
         }
+        // Support the mail parsing system declaring a thread-type
+        elseif (isset($mailinfo['thread-type'])) {
+            switch ($mailinfo['thread-type']) {
+            case 'N':
+                $vars['note'] = $body;
+                $poster = $mailinfo['email'];
+                return $ticket->postNote($vars, $errors, $poster);
+            }
+        }
         // TODO: Consider security constraints
         else {
             $vars['message'] = sprintf("Received From: %s\n\n%s",