revset: added __and__ method to _addset
This method is intended to duck-type baseset, so we will still have _addset as a
private class but we will be able to return it without wrapping it into an
orderedlazyset or a lazyset.
<Include>
<?if $(var.Platform) = "x64" ?>
<?define IsX64 = yes ?>
<?else?>
<?define IsX64 = no ?>
<?endif?>
</Include>