wp_get_attachment_thumb_url-alternative.php

<?
function handsomefox_get_thumbnail($image_url, $size = 'thumbnail') {
  $size = (in_array($size,array('thumbnail','medium','large','full')))
    ? strtolower($size) : 'thumbnail';
  if ($size == 'full')
    return $image_url;

  //break down the file url string
  $ext = pathinfo($image_url, PATHINFO_EXTENSION);
  $file = str_replace('.'.$ext,'',$image_url);
  $ext = strtolower($ext);

  //get the ap width height
  $width = get_option($size.'_size_w');
  $height = get_option($size.'_size_h');

  //replace "jpeg" w wordpress "jpg"
  $ext = ($ext == 'jpeg') ? 'jpg': $ext;

  //reconstruct url
  $thumb = "{$file}-{$width}x{$height}.{$ext}";
  return $thumb;
}