Issue #929166 by dww, deviantintegral, yoroy: Add warning if private files are...

Issue #929166 by dww, deviantintegral, yoroy: Add warning if private files are accessible over the web.

modules/system/system.admin.inc

@@ -1757,7 +1757,7 @@ function system_file_system_settings() {
     '#title' => t('Private file system path'),
     '#default_value' => variable_get('file_private_path', ''),
     '#maxlength' => 255,
-    '#description' => t('A local file system path where private files will be stored. This directory must exist and be writable by Drupal. This directory should not be accessible over the web.'),
+    '#description' => t('An existing local file system path for storing private files. It should be writable by Drupal and not accessible over the web. See the online handbook for <a href="@handbook">more information about securing private files</a>.', array('@handbook' => 'http://drupal.org/handbook/modules/file')),
     '#after_build' => array('system_check_directory'),
   );