rhg: Fall back to Python for bundle repositories rhg does not support bundles at all, yet. Differential Revision: https://phab.mercurial-scm.org/D10102

rhg: Fall back to Python on --repository with an URL A low-hanging fruit to improve on this would be to properly parse and handle `file:` URLs. But other Python-based hg supports some other URL schemes for features that rhg does not support yet. Differential Revision: https://phab.mercurial-scm.org/D10101

rhg: Print non-absolutized path in "repository {} not found" errors … like Python does. Differences in ouput can cause tests to fail. Differential Revision: https://phab.mercurial-scm.org/D10100

rhg: Align "malformed --config" error message with Python Differences in error message formatting can cause tests to fail. Differential Revision: https://phab.mercurial-scm.org/D10099

rhg: Fall back to Python on unsupported `rhg config <section>` Printing an entire section (as opposed to a single value with `rhg config foo.bar`) is not supported yet in Rust only. Differential Revision: https://phab.mercurial-scm.org/D10098

rhg: Fall back to Python for unsupported revset syntax rhg only supports a small subset of the syntax. On parse error, this gives Python a chance instead of aborting immediately. Differential Revision: https://phab.mercurial-scm.org/D10097

tests: Add `rhg` and `no-rhg` for #require and #if in .t files With this we can allow some small differences in expected output between Rust-based and Python-based code paths. Differential Revision: https://phab.mercurial-scm.org/D10096