MDL-24224 fixing a couple more 'strin' typos

lib/enrollib.php

@@ -416,7 +416,7 @@ function enrol_add_course_navigation(navigation_node $coursenode, $course) {
  *   so name the fields you really need, which will
  *   be added and uniq'd
  *
- * @param strin|array $fields
+ * @param string|array $fields
  * @param string $sort
  * @param int $limit max number of courses
  * @return array
@@ -583,7 +583,7 @@ function enrol_get_course_description_texts($course) {
  *
  * @param int $userid
  * @param bool $onlyactive return only active enrolments in courses user may see
- * @param strin|array $fields
+ * @param string|array $fields
  * @param string $sort
  * @return array
  */

lib/filestorage/file_archive.php

@@ -161,7 +161,7 @@ abstract class file_archive implements Iterator {
      * please note that it may fail really badly.
      * The resulting file name is cleaned.
      *
-     * @param strin $localname in another encoding
+     * @param string $localname in another encoding
      * @return string in utf-8
      */
     protected function unmangle_pathname($localname) {