amCharts: wrong url when used with language prefix

Inspired by http://drupal.org/node/879992

Change #459:

    $file = url(
      "${mod_path}/downloaded/${am_category}.swf",
      array('absolute' => TRUE)
    );

to:

    $file = $base_url .'/'. $mod_path ."/downloaded/${am_category}.swf";

Add #192:

    global $base_url;

Sorry I can't profide patch