[interface] Make warning about existing config directory clearer

ChangeLog

@@ -6,6 +6,7 @@ phpMyAdmin - ChangeLog
 + Use indeterminate check all checkbox in server privileges
 + Break server_status.php functions into smaller functions
 + PMA_DBI functions in database_interface.lib.php renamed to be compliant with PEAR standards
++ [interface] Make warning about existing config directory clearer
 
 4.0.1.0 (not yet released)
 - bug #3879 Import broken for CSV using LOAD DATA

index.php

@@ -457,7 +457,7 @@ if (! empty($_SESSION['auto_blowfish_secret'])
  */
 if (file_exists('config')) {
     trigger_error(
-        __('Directory [code]config[/code], which is used by the setup script, still exists in your phpMyAdmin directory. You should remove it once phpMyAdmin has been configured.'),
+        __('Directory [code]config[/code], which is used by the setup script, still exists in your phpMyAdmin directory. It is strongly recommended to remove it once phpMyAdmin has been configured. Otherwise the security of your server may be compromised by unauthorized people downloading your configuration.'),
         E_USER_WARNING
     );
 }