Builds the cancel form for a poll.
function poll_cancel_form($form, &$form_state, $nid) {
$form_state['cache'] = TRUE;
// Store the nid so we can get to it in submit functions.
$form['#nid'] = $nid;
$form['actions'] = array(
'#type' => 'actions',
);
$form['actions']['submit'] = array(
'#type' => 'submit',
'#value' => t('Cancel your vote'),
'#submit' => array(
'poll_cancel',
),
);
return $form;
}