Ensure that ->GotoFirstItem clears the list of "seen" items

Failure to do so would cause the following to fail:
    my $id = $users->First->id;
    $users->GotoFirstItem;
    is( $id, $users->First->id );

...as the firt user would have been marked "already seen" and thus would
be ignored on successive iterations through the collection.
Ensure that ->Count on a fetched collection returns the same number of items ->Next will see