MDL-30018 restore: better answer matching. Credit goes to Tyler Bannister, thanks!

On backup, contents are cleaned to be safe utf8. That was leading to
some matching problems on restore against not cleaned DB contents (for
already existing questions). This commit adds one fallback method to
perform the match against cleaned DB contents.

backup/moodle2/restore_qtype_plugin.class.php

@@ -154,6 +154,22 @@ abstract class restore_qtype_plugin extends restore_plugin {
                        AND ' . $DB->sql_compare_text('answer', 255) . ' = ' . $DB->sql_compare_text('?', 255);
             $params = array($newquestionid, $data->answertext);
             $newitemid = $DB->get_field_sql($sql, $params);
+
+            // Not able to find the answer, let's try cleaning the answertext
+            // of all the question answers in DB as slower fallback. MDL-30018.
+            if (!$newitemid) {
+                $params = array('question' => $newquestionid);
+                $answers = $DB->get_records('question_answers', $params, '', 'id, answer');
+                foreach ($answers as $answer) {
+                    // Clean in the same way than {@link xml_writer::xml_safe_utf8()}.
+                    $clean = preg_replace('/[\x-\x8\xb-\xc\xe-\x1f\x7f]/is','', $answer->answer); // Clean CTRL chars.
+                    $clean = preg_replace("/\r\n|\r/", "\n", $clean); // Normalize line ending.
+                    if ($clean === $data->answertext) {
+                        $newitemid = $data->id;
+                    }
+                }
+            }
+
             // If we haven't found the newitemid, something has gone really wrong, question in DB
             // is missing answers, exception
             if (!$newitemid) {