_adjustlinkrev: reuse ancestors set during rename detection (issue4514) The new linkrev adjustement mechanism makes rename detection very slow, because each file rewalks the ancestor dag. To mitigate the issue in Mercurial 3.3, we introduce a simplistic way to share the ancestors computation for the linkrev validation phase. We can reuse the ancestors in that case because we do not care about sub-branching in the ancestors graph. The cached set will be use to check if the linkrev is valid in the search context. This is the vast majority of the ancestors usage during copies search since the uncached one will only be used when linkrev is invalid, which is hopefully rare.