revlogv2: also test transactionality of revlog v2 Without surprise, this is broken :-) Now that it is tested, we can fix it. Differential Revision: https://phab.mercurial-scm.org/D10627

revlog: add a new test file focussed on testing transactionally issue What we test here is currently also covered by `test-hooks.t`. However having our own test file allow for more focussed/deep testing and to cover more variant when relevant. So we create a new test file. Differential Revision: https://phab.mercurial-scm.org/D10626

revlogv2: store version information in the docket only Having it duplicated in the index was both useless and a risk of discrepancy. Differential Revision: https://phab.mercurial-scm.org/D10625

revlogv2: introduce a very basic docket file This is the first stone toward using a docket file in revlogv2. Right now the docket is very basic and only store the version number (which is -also- stored into the index file…) and the other files have fixed name. This new implementation break transactionally… but they are no test checking transactionally for revlogv2… So I take this as an opportunity to start small. They are no usage of revlogv2 outside of tests anyway. The docket keeps the `.i` naming used by previous version index to preserve a unique entry point. We could decide to use a different name and look it up first, or to fully rework this in a future "store" version. However that does not seems necessary right now. We will re-introduces transactionality (and associated testing…) in a later changesets. A long list of TODOs have been added to the relevant comment. Differential Revision: https://phab.mercurial-scm.org/D10624

branching: merge stable into default

revlogv2: mark revlogv2 as requires a full upgrade This was overlooked previously. Differential Revision: https://phab.mercurial-scm.org/D10623

revlog: unify flag processing when loading index The new code use a simple declaration to do centralised processing. This is clearer, shorter and less error prone. This will be especially useful as we plan to add a fourth format: changelog-v2. Differential Revision: https://phab.mercurial-scm.org/D10622

revlog: unify checks for supported flag The new code use a simple declaration to do centralised checking. This is clearer, shorter and less error prone. This will be especially useful as we plan to add a fourth format: changelog-v2. Differential Revision: https://phab.mercurial-scm.org/D10621

side-data: drop the associated config and requirements This is no longer and extensions of revlog v1, but a part of revlog v2. We no longer needs independent config and requirement management for that. Differential Revision: https://phab.mercurial-scm.org/D10620

revlog: fix capitalisation of an error We don't start error message with capital letters. Differential Revision: https://phab.mercurial-scm.org/D10619