localrepo: reuse parent manifest in commitctx if no files have changed This speeds up the in-memory version of debugbuilddag that I'm working on considerably for the case where we want to build just a 00changelog.i (for discovery tests, for instance). There are a couple of test changes because node ids in tests have changed. The changes to the patch names in test-mq-qdelete.t were required because they could collide with nodeid abbreviations and newly actually do (patch "c" collides with id "cafe..." for patch "b"). [ original upstream description ]