clone: test local clone in `test-clone-uncompressed.t` too This is not an uncompressed test but needs to be tested in the same kind of constraints regarding special file name. Differential Revision: https://phab.mercurial-scm.org/D11218

test-transaction-safety: relax some of the synchronisation schedule We can have `internal` and `external` runs at the same time, so we unlock `external` a bit sooner. Differential Revision: https://phab.mercurial-scm.org/D11216

test-transaction-safety: document the test schedule This helps reader to understand how the test work and actually helped me to detect a missing synchronisation step. Differential Revision: https://phab.mercurial-scm.org/D11215

rhg: Propagate permission errors when finding a repository The Rust standard library has a `Path::is_dir` method that returns false for any I/O error (such as a permission error), not just "No such file or directory". Instead add an `is_dir` function that returns false for non-directories and for "No such file or directory" errors, but propagates other I/O errors. Differential Revision: https://phab.mercurial-scm.org/D11230

rhg: Add build and config instructions to the README file This adds documentation explaining how to compile, configure, and use rhg as well as how the fallback mechanism works. Differential Revision: https://phab.mercurial-scm.org/D11229

dirstate: use `add` in the deprecation message about `add` The previous message was talking about `remove`. Differential Revision: https://phab.mercurial-scm.org/D11224