Correct the subscription user regex FS#2250

This fixes the subscription user regex to really only not to match the
author of the change but to still match users who have that username as
substring in their username.

inc/subscription.php

@@ -278,8 +278,8 @@ function subscription_addresslist(&$data){
     }
     $pres = array('style' => 'every', 'escaped' => true);
     if (!$self && isset($_SERVER['REMOTE_USER'])) {
-        $pres['user'] = '((?:(?!' . preg_quote_cb($_SERVER['REMOTE_USER']) .
-                        ')\S?)+)';
+        $pres['user'] = '((?!' . preg_quote_cb($_SERVER['REMOTE_USER']) .
+                        '\b)\S+)';
     }
     $subs = subscription_find($id, $pres);
     $emails = array();