[1.7.0] Add DefinitionCache decorators, implement Memory decorator

- Move serialization responsibility to Config
- Create DefinitionCacheFactory
- Implement Null definition cache

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@1117 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/DefinitionCache/Null.php

@@ -0,0 +1,37 @@
+<?php
+
+require_once 'HTMLPurifier/DefinitionCache.php';
+
+/**
+ * Null cache object to use when no caching is on.
+ */
+class HTMLPurifier_DefinitionCache_Null extends HTMLPurifier_DefinitionCache
+{
+    
+    function add($def, $config) {
+        return false;
+    }
+    
+    function set($def, $config) {
+        return false;
+    }
+    
+    function replace($def, $config) {
+        return false;
+    }
+    
+    function get($config) {
+        return false;
+    }
+    
+    function flush() {
+        return false;
+    }
+    
+    function cleanup($config) {
+        return false;
+    }
+    
+}
+
+?>