Allow localización

Great module, just a comment on localization: t() is not used everywhere it should be, for example views_calc_calc_options() should read:

function views_calc_calc_options() {
  return array('SUM' => t('Sum'), 'COUNT' => t('Count'), 'AVERAGE' => t('Average'), 'AVERAGE_ALL' => t('Average (all)'));
}

There might be other places where t() should be used. If i find more, i'll post a comment on this thread.
Cheers.