path: forbid chaining `path://` definitions To have `path://xxx` referencing paths that use `path://` too, we need to analyze dependencies to initialize them in the right order (and to detect cycle). I don't want to deal with that right now, so I just disallow it for now. Differential Revision: https://phab.mercurial-scm.org/D10264

path: introduce a `path://` syntax to reference other path name This make it easier for a path to reuse the same location of another path with different parameter. This is useful to create path "alias" with common config option. This will become very useful to create path that reference a list of other path. This changeset focus on implemented the basic feature, future changesets will deal with various error management (and associated testing). Differential Revision: https://phab.mercurial-scm.org/D10263

path: extract sub-option logic into its own method We will need to re-use this logic for `path://` so we first extract it into its own method. Differential Revision: https://phab.mercurial-scm.org/D10262

path: extract the path validation logic into its own submethod We will need to re-use this logic for `path://` so we first extract it into its own method. Differential Revision: https://phab.mercurial-scm.org/D10261

path: move handling of "default" (*) suboptions value inside __init__ With the introduction of `path://` scheme the handling of default value will need to be subtler. We do simple code movement first to clarify the future changes. Differential Revision: https://phab.mercurial-scm.org/D10260

rhg: Initial support for the 'status' command Only comparing the working directory with its first parent revision is supported. The core logic of dirstate handling and `stat`’ing files was already in `hg-core` supporting Python-based hg with Rust extensions, so this is mostly plumbing to rhg’s CLI. For now the command is experimental and disabled by default, since it has some bugs that causes a number of tests to fail. These failures can be seen with: tests/run-tests.py --rhg --extra-config-opt rhg.status=true Differential Revision: https://phab.mercurial-scm.org/D10239

rhg: raise wdir specific error for `hg debugdata` Helps remove the conditional in `test-debugcommands.t` for rhg. Differential Revision: https://phab.mercurial-scm.org/D10254