Recursively converts a tree of menu links to a flat array.
$tree: A tree of menu links in an array.
$flat: A flat array of the menu links from $tree, passed by reference.
function _book_flatten_menu($tree, &$flat) {
foreach ($tree as $data) {
if (!$data['link']['hidden']) {
$flat[$data['link']['mlid']] = $data['link'];
if ($data['below']) {
_book_flatten_menu($data['below'], $flat);
}
}
}
}