You just need to override theme_pager_previous()
and theme_pager_next()
(easiest to do in your theme):
function MYTHEME_pager_previous($vars) {
$text = $variables['text'];
$element = $variables['element'];
$interval = $variables['interval'];
$parameters = $variables['parameters'];
global $pager_page_array;
$output = '';
// If we are anywhere but the first page
if ($pager_page_array[$element] > 0) {
$page_new = pager_load_array($pager_page_array[$element] - $interval, $element, $pager_page_array);
// Changes from core function start here.
$attributes = array('rel' => 'prev');
// If the previous page is the first page, mark the link as such.
if ($page_new[$element] == 0) {
$output = theme('pager_first', array('text' => $text, 'element' => $element, 'parameters' => $parameters, 'attributes' => $attributes));
}
// The previous page is not the first page.
else {
$output = theme('pager_link', array('text' => $text, 'page_new' => $page_new, 'element' => $element, 'parameters' => $parameters, 'attributes' => $attributes));
}
}
return $output;
}
And the same thing for pager_next.