drupal_goto( 'user/login',drupal_get_destination() );

if you want to set destination from url than

set destination of current page

$dest= drupal_get_destination();

<a href="<?php print get_base_url()?>/user/login?<?php echo $dest; ?>"> // login

<a href="<?php print get_base_url()?>/user/register?<?php echo $dest; ?>" //register

and change $form_state[‘redirect’]  in core user module, in the function user_login_submit() and user_register_submit()

#and change

if(isset($_GET[‘destination’]) && !empty($_GET[‘destination’]))
$dest = $_GET[‘destination’];
$dest = ‘home’;
$form_state[‘redirect’] = $dest;

or just

$dest = $_GET[‘destination’];

$form_state[‘redirect’] = $dest;

in user_register_submit() set this code under Registration successful and Your password and further instructions have been sent to your e-mail address messages.