When trying to view the participants page for a course that has both:
a) a 'Random glossary entry' block; and
b) at least one entry in that block;
Trying to view the 'course participants' page fails.

Expected Output: Participants page displays.
Actual Output: "Fatal error: Call to undefined function file_rewrite_pluginfile_urls() in /var/www/html/moodle20/blocks/glossary_random/block_glossary_random.php on line 95" (or a blank page if debugging is off).

Seems all thats needed is to require the filelib.php at the start of the function.

diff --git a/blocks/glossary_random/block_glossary_random.php b/blocks/glossary_random/block_glossary_random.php

index 4764430..19aa1d8 100644

--- a/blocks/glossary_random/block_glossary_random.php

+++ b/blocks/glossary_random/block_glossary_random.php

@@ -11,6 +11,7 @@ class block_glossary_random extends block_base {

     function specialization() {

         global $CFG, $DB;

+        require_once($CFG->libdir . '/filelib.php');

         $this->course = $this->page->course;