Twenty Eleven Headers Swapout

<?php
add_action( 'after_setup_theme', 'dr_post_theme_setup' );
if ( !function_exists( 'dr_post_theme_setup' ) ):
function dr_post_theme_setup() {

    /* Remove the twenty eleven default Headers */
    function dr_update_twenty_eleven_headers(){
        unregister_default_headers( array(
            'wheel',
            'shore',
            'trolley',
            'pine-cone',
            'chessboard',
            'lanterns',
            'willow' ,
            'hanoi')
            );

        // Register default custom headers packaged with the child theme.
        $headers = dr_default_headers();
        if( $headers ) register_default_headers( $headers );
    }
    add_action( 'after_setup_theme', 'dr_update_twenty_eleven_headers', 11 );
}
endif;

// read through the /images/headers/ to get a list of custom headers.
function dr_default_headers(){
    // Create an empty array
    $list = array();
    // Get the file directory path and url
    $path = get_stylesheet_directory() .'/images/headers/';
    $url = get_stylesheet_directory_uri() .'/images/headers/';
    // Open the /images/headers/ folder
    $dir_handle = @opendir($path) or die("Unable to open $path");
    // Loop through the header images
    while($file = readdir($dir_handle)){
        if($file == "." || $file == ".."){continue;}
        $filename = explode(".",$file);
        $cnt = count($filename); $cnt--; $ext = $filename[$cnt];
        // Is the image a jpg or png
        if(strtolower($ext) == ('png' || 'jpg')){
            // if the image is post fixed with -thumbnail add it to the array
            if ( strpos($file, '-thumbnail') > 0 ) {
                $name = substr($file, 0, strpos($file, '-thumbnail') );
                $list[$name] = array(
                    'url' => $url .$name .'.' .$ext,
                    'thumbnail_url' => $url .$file,
                    'description' => __( ucwords( str_replace("-"," ",$name) ), 'twentyeleven' )
                );
            }
        }
    }
    return $list;
}