merge patch from https://sourceforge.net/p/postfixadmin/bugs/347/ (thank you Eugene Grosbein) - explictly set session_cache_limiter to nocache

git-svn-id: https://svn.code.sf.net/p/postfixadmin/code/trunk@1792 a1433add-5e2c-0410-b055-b7f2511e0802

common.php

@@ -20,6 +20,8 @@ if(!defined('POSTFIXADMIN')) { # already defined if called from setup.php
     define('POSTFIXADMIN', 1); # checked in included files
 
     if (!defined('POSTFIXADMIN_CLI')) {
+        // this is the default; see also https://sourceforge.net/p/postfixadmin/bugs/347/
+        session_cache_limiter('nocache'); 
         session_start();
 
         if (defined('POSTFIXADMIN_LOGOUT')) {