PERF logging - move handling to moodle_request_shutdown()

By moving the performance profile logging to the very
end of PHP processing, we cover more pages, notably those
that don't end up with a footer or a redirect, like file
serving.

This should improve quality of our performance logs, and
help catch some piggies...

lib/setup.php

@@ -227,7 +227,7 @@ global $HTTPSPAGEREQUIRED;
 
 
 /// For now, only needed under apache (and probably unstable in other contexts)
-    if (function_exists('apache_child_terminate')) {
+    if (function_exists('register_shutdown_function')) {
         register_shutdown_function('moodle_request_shutdown');
     }