revset: drop argument when it's None getstack's definition is `getstack(repo, rev=None)`, so providing None explicitly is unnecessary. Moreover, when x is not None, it's definitely not a revision but a part of a parsed tree of revset arguments. Differential Revision: https://phab.mercurial-scm.org/D6707

stack: remove unnecessary reverse() predicate Stack already sorts revisions, so no need to do it twice. This change was a part of D2400, which didn't land for other reasons. See also D2399, where this change was suggested. Differential Revision: https://phab.mercurial-scm.org/D6706

automation: increase root volume size on Linux It is close to full in the AMI. I actually ran out of space running tests without increasing the volume size! Differential Revision: https://phab.mercurial-scm.org/D6716

automation: install Rust in Linux environment This will install Rust 1.31.1, 1.34.2, and whatever stable is at the time the install runs. We install 1.31.1 as our minimum supported Rust version (I think that's what we're currently targeting) and 1.34 because that's what Debian 10 is shipping. Differential Revision: https://phab.mercurial-scm.org/D6715

automation: update packages in requirements files We like keeping up to date. The content of the autogenerated files changed slightly because I used a newer version of `pip-compile` than what was used previously. Differential Revision: https://phab.mercurial-scm.org/D6714

automation: install latest Python versions This required bumping the pyenv commit so the new versions are available. Differential Revision: https://phab.mercurial-scm.org/D6713

upgrade: introduce the internal code for revlog cloning selection For now we still clone every single revlogs but all the selection mechanism is now in place in the lower layer. The next changesets will introduce the user interface part of the selection.