repo-upgrade: write new requirement before upgrading the dirstate This will prevent a small race condition where another hg process still believes the repo is dirstate-v1 during the upgrade process. This is good to have, but it is not a proper fix for the underlying problem. There is code that assumes a requirement means a usage, e.g. having the `generaldelta` requirement would imply *all* revlogs to use general delta, but it's not true, it simply means that the repository advertises to the client it needs to understand `generaldelta` in order to read the repo. In the case of the dirstate, having the requirement *technically* should always be the same as using dirstate-v2, since there is only one dirstate and requirements should be as minimal as possible. However, we should not assume this and make the code more robust in a future patch (series).