changelog: change the implementation of `_divertopener` During a transaction, new data to the changelog index are "diverted". The previous implementat ways pretty basic, we need something better to be able to use the changelog vfs fully during transaction. (eg: accessing the vfs options). Differential Revision: https://phab.mercurial-scm.org/D8185

nodemap: test that an outdated nodemap can catch up If the persistent nodemap does not contains all revision that the index contains, this is should be detected and dealt with. We add a test for this case. Differential Revision: https://phab.mercurial-scm.org/D8183

nodemap: document the docket attributes More documentation rarely hurts. Differential Revision: https://phab.mercurial-scm.org/D8182

git: key off `git` in .hg/requires rather than separate file Differential Revision: https://phab.mercurial-scm.org/D8265

git: correctly handle p1() on dirstate when underlying git repo is empty This shows up in my next change, which ends up making an empty git repo and then running hg. Differential Revision: https://phab.mercurial-scm.org/D8271

rust: clean remains of direct-ffi code Since b55bec1ea972, the cext entry poitn have been removed, so we drop the code for consistency.

heptapod-ci: use the new `--rust/--no-rust` flag to run the tests

run-tests: add option for running with and without Rust extensions This provide a simple and clear way to run the test with or without rust.

run-tests: rename "pure" variable to setup_opts There are more useful flag than just `--pure`. We clarify the variable name before adding more options.

setup-rust: add a --no-rust flag This new flag will make sure the rust extension will not be build. If neither `--rust` nor `--no-rust` is specified the `HGWITHRUSTEXT` is used.