changelogv2: use a dedicated on disk format for changelogv2 We drop two unused entry. This is mostly a proof of concept before starting to actually rework the format. Differential Revision: https://phab.mercurial-scm.org/D10667

revlog: do not call Rust code if the index is not compatible with it This will avoid hitting the TypeError we defined in the previous changesets. This is the simplest fix but not the most elegant. Ideally we would teach the Rust code to use any kind of revlog. However this is an adventure for another time. Differential Revision: https://phab.mercurial-scm.org/D10666

revlog: signal which revlog index are compatible with Rust Otherwise, Rust may treat python object like `cindex` object, leading to trouble. The new attribute is an integer because I expect we might need a flag field in the future. As a start we get the rust code to raise a clear TypeError. We will use the information in a smarter way in the next changesets. Differential Revision: https://phab.mercurial-scm.org/D10665

revlog: pass around the `rev` we deal with when packing/unpacking entry This will help code to compute some flag on the fly. Differential Revision: https://phab.mercurial-scm.org/D10664