_descendants: directly use smartset As `addset` objects are proper smartset objects, we do not need to make any transformation of the result.

baseset: explicitly track order of the baseset A baseset starts without an explicit order. But as soon as a sort is requested, we simply register that the baseset has an order and use the ordered version of the list to behave accordingly. We will want to properly record the order at creation time in the future. This would unlock more optimisation and avoid some sorting.

baseset: fix isascending and isdescending We now have sufficient information to return the proper value there.

baseset: prepare lazy ordering in __iter__ We'll explicitly track the order of the baseset to take advantage of the ascending and descending lists during iteration.

baseset: implement a fastasc and fastdesc Baseset contains already-computed revisions. It is considered "cheap" to do operations on an already-computed set. So we add attributes to hold version of the list in ascending and descending order and use them for `fastasc` and `fastdesc`. Having distinct lists is important to provide correct iteration in all cases. Altering a python list will impact an iterator connected to it. eg: not preserving order at iterator creation time >>> l = [0, 1] >>> i = iter(l) >>> l.reverse() >>> list(i) [1, 0] eg: corrupting in progress iteration >>> l = [0, 1] >>> i = iter(l) >>> i.next() 0 >>> l.reverse() >>> i.next() 0

baseset: stop inheriting from built-in list class The baseset is doing more and more smartset magic and using its list-like property less and less. So we store the list of revisions in an explicit attribute and stop inheriting. This requires reimplementing some basic methods.

strip: stop calling `remove` on smartset The `remove` method is not part of the smartset specification. We use a plain old list comprehension instead.

rebase: transform the smartset to a list before comparing with a list This is highly suboptimal but smartsets are not comparable to lists yet.

merge.update: use `first` instead of direct indexing This makes it compatible with all smartset classes.

qimport: use `first` and `last` instead of direct indexing This makes it compatible with all smartset classes.