User navigation code cleanup

Items that Dan pointed out:

1. user/classes/output/myprofile/manager.php - Remove including the lib file

   // Add core nodes.

   $file = $CFG->libdir . "/myprofilelib.php";

   if (is_readable($file)) {

   require_once($file);

2. grade/report/mygrades.php - Remove MOODLE_INTERNAL and put in a require_login check.
3. lib/output*.php - Clear up confusion about $imagedata in the phpdocs, at the moment they don't agree with each other (render class phpdocs).
4. course/user.php - perhaps include a developer debug message for the default at the end of the page. Re-word the comment.