Make YamlFileLoader and XmlFileLoader file loading extensible

By changing visibility to protected it becomes possible to extend the
loader and cache file contents. phpBB needs this.

src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php

@@ -204,7 +204,7 @@ class XmlFileLoader extends FileLoader
      *
      * @throws \InvalidArgumentException When loading of XML file returns error
      */
-    private function parseFile($file)
+    protected function parseFile($file)
     {
         $internalErrors = libxml_use_internal_errors(true);
         $disableEntities = libxml_disable_entity_loader(true);

src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php

@@ -233,7 +233,7 @@ class YamlFileLoader extends FileLoader
      *
      * @return array The file content
      */
-    private function loadFile($file)
+    protected function loadFile($file)
     {
         return $this->validate(Yaml::parse($file), $file);
     }