dirstate: add v1-v2 variants to the dirstate's read race tests More cases mean different issues.

dirstate: check dirstate race condition around status More problems to solve.

dirstate: check dirstate race condition around update More problems to solve.

dirstate: check dirstate race condition around commit Once in a while, rhg is the only one to behave right here.

dirstate: initial creation of a test file to check dirstate race read More problems to solve… yeah ! (I guess)

dirstate: add a synchronisation point before doing a full dirstate read This will be useful to test some race conditions around the dirstate.

rust-repo: move dirstate-v2 opening to a separate method The next changeset will make changes to this logic, it helps to have it in order first.

rhg: fix race when an ambiguous file is deleted on disk There are two places in the status code where we handle files whose status we are unsure of based off of metadata alone: this one is the first one to actually disambiguate, and the second one is later in the code (but updated in the previous commit) for files that are actually clean to update the dirstate. Since there is a chance that the contents have changed between those two moments, we need to stat the files again, since re-using the old stat could lie about the clean state of the file.

rhg: fix race when a fixup file is deleted on disk See next changeset for the other race in the same kind of logic and why there are two different places.

dirstate: test a `hg status` raced by a `hg remove` This shows that `rhg` is misbehaving here.