tracked-file: rename the format option to use `use-` This is more consistent with the other options. Differential Revision: https://phab.mercurial-scm.org/D12200

tracked-key: update the requirement value We renamed the config option but we forgot to change the actual value… Differential Revision: https://phab.mercurial-scm.org/D12199

tracked-key: make it possible to upgrade to and downgrade from the feature This seems rather important if we want people to start using it. Differential Revision: https://phab.mercurial-scm.org/D12198

obsolete: don't use os.stat in repo.obsstore.__nonzero__ if it's static HTTP If a repo is accessed via static HTTP, then we obviously can't use os.stat() to just peek at the file size. Let's download the entire file to check its size. Yes, this feels wasteful, but: 1. If we're cloning or pulling a repo from a static HTTP server, we need the contents of the obsstore anyway. 2. Implementing statichttpvfs.stat() that uses HEAD will result in one more request to a static-only HTTP server, which is already slow. Also parsing a response to a HEAD request to construct os.stat_result is pretty hacky. There's also a question of the remote server properly supporting HEAD method and reporting at least file size. 3. Implementing statichttpvfs.stat() that uses GET is pretty much the same thing as we do here, except we can't even cache the response easily, unlike simply accessing obsstore._data, which is @propertycache'd. Importing statichttprepo locally to avoid circular import. See also: 4507bc001365 and commit message of f8f2ecdde4b5. Differential Revision: https://phab.mercurial-scm.org/D12195