obsutil: fix the issue5686 While traversing the obsolescence graph to find the successors sets of csets: In its 4th case (read comments of obsutil.successorssets to see all 4 cases) where we know successors sets of all direct successors of CURRENT, we were just missing a condition to filter out the case when a cset is pruned. And without this condition (that this patch added) it was making a whole successor set to [] just because of one pruned marker. For e.g:if following is the successors set of a cset A: A -> [a, b, c] if we prune c, we expect A's successors set to be [a, b] but you would get: A -> [] So this patch make sure that we calculate the right successorsset of csets considering the pruned cset (in split case). Differential Revision: https://phab.mercurial-scm.org/D5474