rust: pure Rust lazyancestors iterator This is the first of a patch series aiming to provide an alternative implementation in the Rust programming language of the _lazyancestorsiter from the ancestor module. This iterator has been brought to our attention by the people at Octobus, as a potential good candidate for incremental "oxydation" (rewriting in Rust), because it has shown performance issues lately and it merely deals with ints (revision numbers) obtained by calling the index, whih should be directly callable from Rust code, being itself implemented as a C extension. The idea behind this series is to provide a minimal example of Rust code collaborating with existing C and Python code. To open the way to gradually rewriting more of Mercurial's Python code in Rust, without being forced to pay a large initial cost of rewriting the existing fast core into Rust. This patch does not introduce any bindings to other Mercurial code yet. Instead, it introduces the necessary abstractions to address the problem independently, and unit-test it. Since this is the first use of Rust as a Python module within Mercurial, the hg-core crate gets created within this patch. See its Cargo.toml for more details. Someone with a rustc/cargo installation may chdir into rust/hg-core and run the tests by issuing: cargo test --lib The algorithm is a bit simplified (see details in docstrings), and at its simplest becomes rather trivial, showcasing that Rust has batteries included too: BinaryHeap, the Rust analog of Python's heapq does actually all the work. The implementation can be further optimized and probably be made more idiomatic Rust.

run-tests: restore quoting the python executable for running *.py tests This was accidentally dropped in 8cf459d8b111.

tests: replace `cd ..` with an absolute path in a couple ssh tests These tests are broken under py3 on Windows to the point where the `cd ..` was actually escaping into the system wide $TEMP. The subsequent `hg init` created a repo there, and then added a local extension to the hgrc. This breaks every single subsequent test when it tries to `hg init` in its $TESTTMP, and can't load the localwrite.py extension. And since I botched this the first time and replaced the wrong `cd ..`, this just replaces all of them. I've noticed test garbage in $TEMP recently, and maybe this will help. Perhaps `hg init` shouldn't load the config for the local repo, but this is an easy enough workaround for now.

lfs: register the flag processors per repository Previously, enabling the extension for any repo in commandserver or hgweb would enable the flags on all repos. Since localrepo.resolverevlogstorevfsoptions() is called so early, the check to see if the extension is enabled on the repo (which hasn't been instantiated yet) is a bit awkward. But I don't see a better way.

revlog: allow flag processors to be applied via store options This allows flag processors to be registered to specific repos in an extension by wrapping localrepo.resolverevlogstorevfsoptions(). I wanted to add the processors via a function on localrepo, but some of the places where the processors are globally registered don't have a repository available. This makes targeting specific repos in the wrapper awkward, but still manageable.

py3: use str to query registry values on Windows This blew up launching any command if extdiff processed a tool with a regkey config.

py3: convert "usage" literal to bytes Here _() is practically an identity function, but we shouldn't pass in unicode to _().

churn: remove redundant round() To my surprise, the int() is required. Spotted by Mads when he reviewed D5063. Thanks! Differential Revision: https://phab.mercurial-scm.org/D5086

py3: use py3 as the test tag, dropping the k Differential Revision: https://phab.mercurial-scm.org/D5079

tests: fix inline extension in test-fncache.t for Python 3 # skip-blame just some b prefixing Differential Revision: https://phab.mercurial-scm.org/D5083

py3: 3 more passing tests Differential Revision: https://phab.mercurial-scm.org/D5082

simplemerge: port to Python 3 Differential Revision: https://phab.mercurial-scm.org/D5081