Implements hook_comment_update().
Comment module doesn't call hook_comment_unpublish() when saving individual comments so we need to check for those here.
function tracker_comment_update($comment) {
// comment_save() calls hook_comment_publish() for all published comments
// so we need to handle all other values here.
if ($comment->status != COMMENT_PUBLISHED) {
_tracker_remove($comment->nid, $comment->uid, $comment->changed);
}
}