re2: fix reporting of availability in `hg debuginstall` We add and use an official API to check is re2 is available. This prevent the bug previously in place were debuginstall was considering confusing `None` (i.e. non-initialized) and `False` (i.e. unavailable).

re: make _checkre2 a static method There is no need to it to be a method, so we make it at least a static method to make it easier to call.

re2: exit `_checkre2` early if calling it is useless If we already know if re2 is supported there is no need to run the check again. Stricly speaking we don't call it twice, but this seems a simple enough safeguard to include in this series.

test-dirstate-version-fallback: future-proof the test for a different default Dirstate-v2 will become the default at some point, which would cause this test to fail. Let's save someone else the headache later.

Added signature for changeset da372c745e0f

Added tag 6.4.4 for changeset da372c745e0f

relnotes: add 6.4.4

revlog: avoid possible collision between directory and temporary index Since 6.4, we create a temporary index file to write the split data without overwriting the inline version too early. However, the store encoding does not prevent these new `.i.s` file to collide with a directory with the same name. While the odds for such a collision to happens are fairly low, the collision would prevent Mercurial from working. The store encoding have a mitigation solution in place to prevent such collisions from happening for `.i` and `.d` files, but not for other extensions. We cannot update this encoding scheme to solve the issue since it would diverge from older version of Mercurial. Instead, we create an alternative directory tree dedicated to such files. The use of the `.i` extension combined with store encoding will prevent collisions there.

revlog: move the computation of the split_index path in a property This is about to become more complex, so we gather the logic in a single place.

rust-dirstate: fall back to v1 if reading v2 failed This will help us not fail when a v1 dirstate is present on disk while a v2 was expected (which could happen with a racy/interrupted upgrade).