Add $uid as optional variable to buddylist_add($id)

buddylist_add is currently written as

function buddylist($id) {
  global $user
....
}

this patch changes it to

function buddylist($id, $uid = NULL) {
if (is_null($uid)) {
global $user;
}
...
}


in short it allows a buddy to be assigned between two arbitrary people instead of a new buddy with the currently logged in user. As a case example when saving buddy relationship with a newly signed up user via hook_user the $user object is set to anonymous because the newly signed up user isn't signed IN... but you know their ID ;)