retry()
  Retry scanner more times.
  
  This scanner try to run defined scanner more than once, while if fails.
  After an successful pass latest return value is returned.
  
  Usage: retry(count,scanner())
  
  Where: count is an integer, which defines retry count
         scanner(),... is a scanner, which may find a virus
  
  Example: retry(5,
             alternatives(
               spamassassind(...),
               spamassassind(...)
             )
           )