Gets a book menu link by its menu link ID.
Like menu_link_load(), but adds additional data from the {book} table.
Do not call when loading a node, since this function may call node_load().
$mlid: The menu link ID of the menu item.
A menu link, with the link translated for rendering and data added from the {book} table. FALSE if there is an error.
function book_link_load($mlid) {
return entity_load('menu_link', $mlid);
}