evolve: make _computeobsoleteset() return a frozenset Let's make sure that obsolete.getrevs(repo, b'obsolete') returns a frozenset to be compatible with Mercurial 6.1. This shouldn't produce any issues on older versions, because I doubt anything tries to modify a set of obsolete revisions by calling .add() or .remove() directly on it. See 27fe84a8dd60 and c7e675848027 in core.