revset: improve head revset performance Previously the head() revset would iterate over every item in the subset and check if it was a head. Since the subset is often the entire repo, this was slow on large repos. Now we iterate over each item in the head list and check if it's in the subset, which results in much less work. hg log -r 'head()' on a large repo: Before: 0.95s After: 0.28s

revset: added ascending attribute to addset class In case both collections are in an ascending/descending order then we will be able to iterate them lazily while keeping the order.

revset: added set method to addset to duck type generatorset Since this class is only going to be used inside revset.py (it does not duck type baseset) it needs to duck type only a few more methods for the next patches.