WordPress Link Library Patch to support Hierarchical Links

function link_library_cats_recursive_func($cats=null) {
    if (!empty($cats)) {
        // A place to store the extended list
        $hierarchy = array();
        // Original selection passed to plugin
        $cats_selected = explode(',', $cats);
        // Ask WordPress for a list of all link categories
        $cats_all = get_terms('link_category');
        // Loop through all passed categories for children
        foreach($cats_selected as $category) {
            // A place to store the children
            $subcat = array();
            // Check all categories to see if their parent was passed to this function
            foreach($cats_all as $cat_obj) {
                // If so...
                if ($category == $cat_obj->parent) {
                    // ... collect the id
                    $subcat[] = $cat_obj->term_id;
                }
            }
            // If we collected any children (id)...
            if (!empty($subcat)) {
                // ... run this function recursively looking for more
                $nest = $this->link_library_cats_recursive_func(implode(',', $subcat));
                // And if we found any more...
                if (!empty($nest)) {
                    // ... put them with the rest of the children
                    $subcat= array_unique(array_merge($subcat, explode(',', $nest)));
                }
            }
            // Add the children ids to the extended list of categories
            $hierarchy = array_unique(array_merge($hierarchy, $subcat));
        }
        // Merge list of extended categories with those originally passed
        $result = array_unique(array_merge($hierarchy, $cats_selected));
        // Return list as a comma-seperated list so the plugin can carry on
        return implode(',', $result);
    }
}