rust: introduce Repo and Vfs types for filesystem abstraction This is similar to the corresponding Python classes. Repo represents a repository and knows the path to the `.hg` directory, the `store` directory, and the working directory. Separating these will enable supporting the share extension. A Vfs is created from a Repo for one of these three directories. It has filesystem access APIs that take a relative std::path::Path as a parameter. Differential Revision: https://phab.mercurial-scm.org/D9596

bundle2: drop some outdated comment This commend trace back to a very early bundle2 changeset c7ceae0faf69. And the code moved past this warning over 5 years ago. Differential Revision: https://phab.mercurial-scm.org/D9637

bundle: optional advisory obsolescence parts It is useful to ship obsolescence markers as part of clonebundles or pullbundles, but they shouldn't stop a non-evolution client from working. Differential Revision: https://phab.mercurial-scm.org/D8480

relnotes: document that `hg extdiff` also got -r replaced by --from/--to Differential Revision: https://phab.mercurial-scm.org/D9628

hghave: add some official category for known-bad and missing-good output This will make it simple to tag output that are expected to changes. A simple hghave integration seems enough but smarter behavior around these seems possible in the future. Differential Revision: https://phab.mercurial-scm.org/D9607

copies: rename value/other variable to minor/major for clarity Differential Revision: https://phab.mercurial-scm.org/D9591