revset: changed smartset methods to return ordered addsets Now when adding two structures that are ordered, they are wrapped into an _addset and they get added lazily while keeping the order.

revset: added isascending and isdescending methods to _addset This methods are intended to duck-type baseset, so we will still have _addset as a private class but now we can return it without wrapping it into an orderedlazyset or a lazyset. These were the last methods to add for smartset compatibility.