rebase: use one dirstateguard for entire rebase Recently we switched rebases to run the entire rebase inside a single transaction, which dramatically improved the speed of rebases in repos with large working copies. Let's also move the dirstate into a single dirstateguard to get the same benefits. This let's us avoid serializing the dirstate after each commit. In a large repo, rebasing 27 commits is sped up by about 20%. I believe the test changes are because us touching the dirstate gave the transaction something to actually rollback.