destutil: if wdp is obsolete, update to the closest non-obsolete ancestor As the original comments suggest, using prune as a model here was an existing idea, and now this patch implements it. I think it would be even better to do what solveobswdp() from evolve does (in short, it allows to update to a successor of the closest ancestor even if that ancestor is obsolete), but that is outside of this series' scope. Differential Revision: https://phab.mercurial-scm.org/D12099