/**
  * Return combined minified content for a set of sources
  *
  * No internal caching will be used and the content will not be HTTP encoded.
  * 
  * @param array $sources array of filepaths and/or Minify_Source objects
  * 
  * @param array $options (optional) array of options for serve. By default
  * these are already set: quiet = true, encodeMethod = '', lastModifiedTime = 0.
  * 
  * @return string
  */
 public static function combine($sources, $options = array())
 {
     $cache = self::$_cache;
     self::$_cache = null;
     $options = array_merge(array('files' => (array) $sources, 'quiet' => true, 'encodeMethod' => '', 'lastModifiedTime' => 0), $options);
     $out = self::serve('Files', $options);
     self::$_cache = $cache;
     return $out['content'];
 }