Add a supp download button and fix the dl llink

added a case for a supplemental file attachment to the full record view.
the link in the template file seems to be broken and this code may fix.
both need to be tested.
it looks like the problem is lower level than this.  The $dl_pid is not available to use and even the $variables['pid'] will fail as it looks like instead of adding new elements to the variables array in the preprocessor we are actually over writing it.

`$variables = array(
    'datastream_array' => $datastream_array,
    'zip_description' => $description,
    'zip_size' => $datastream_info->datastream->size,
    'zip_array' => $supp_array,
    'supp_header' => $supp_header,
    'supp_rows' => $supp_rows,
  );`