Cater for destination query string paremeter when using drupal_goto()

`drupal_goto()` will check to see if there's a `destination` query string parameter and will redirect there if present, so going to `/raven/login?destination=foo` will go to `foo` rather than to Raven. This stores the parameter as the redirect page, so that after going to Raven the user will go to `foo`.

Like `drupal_goto()` it makes sure that it's not an absolute URL.