MDL-40903 cache: coding style tidyup pre-integration

cache/classes/definition.php

@@ -726,7 +726,7 @@ class cache_definition {
      *
      * Please call data_should_be_persistent instead.
      *
-     * @deprecated since 2.6
+     * @deprecated since 2.4.7
      * @return bool
      */
     public function should_be_persistent() {
@@ -734,7 +734,11 @@ class cache_definition {
     }
 
     /**
-     * Returns true if the cache loader for this definition should be persistent.
+     * Returns true if we should hold onto the data flowing through the cache.
+     *
+     * If set to true data flowing through the cache will be stored in a static variable
+     * to make subsequent requests for the data much faster.
+     *
      * @return bool
      */
     public function data_should_be_persistent() {
@@ -844,4 +848,4 @@ class cache_definition {
     protected function get_cache_identifier() {
         return cache_helper::get_site_identifier();
     }
-}
+}