preferred item image size for theme, get smallest photo near scale requested

preferred item image size for theme, get smallest photo near scale requested

themes can declare preferred image size for images in items, with

   $a->theme_info = array(
    "item_image_size" => 1
   );

0: original, 1:640px, 2:320px

mod/photo.php returns the nearest scaled image near requested one
if it doesn't exists, instead of nothing