MDL-15635 DTL refactoring, adding release field to xml file

lib/dtl/string_xml_database_exporter.php

@@ -0,0 +1,37 @@
+<?php  //$Id$
+
+/**
+ * XML format exporter class to memory storage (i.e. a string).
+ */
+class string_xml_database_exporter extends xml_database_exporter {
+    /** String with XML data. */
+    protected $data;
+
+    /**
+     * Specific output method for the memory XML sink.
+     */
+    protected function output($text) {
+        $this->data .= $text;
+    }
+
+    /**
+     * Returns the output of the exporters
+     * @return string XML data from exporter
+     */
+    public function get_output() {
+        return $this->data;
+    }
+
+    /**
+     * Specific implementation for memory exporting the database: it clear the buffer
+     * and calls superclass @see database_exporter::export_database().
+     *
+     * @exception export_exception if any checking (e.g. database schema) fails
+     * @param string $description a user description of the data.
+     * @return void
+     */
+    public function export_database($description=null) {
+        $this->data = '';
+        parent::export_database($description);
+    }
+}