wget.callbacks.httploop_proceed_p can script local filenames

    by returning a table (implies PROCEED) with:
 
      * local_filename="string"
        this will override extensions set by -E unless:
 
      * override_fiilename=0
        is set
 
    example:
 
    wget.callbacks.httploop_proceed_p = function(url, http_stat)
      return {
        local_file="foobar/"..http_stat.local_file.."silly_ext",
        override_filename=1
      }
    end