dirstate: align Rust function name to `need_delay` The rest of the code use this name. It is not a great name, but it is better to stay consistent. Differential Revision: https://phab.mercurial-scm.org/D11699

dirstate: rename a `very_likely_equal` method to `likely_equal` No need to oversell it. Differential Revision: https://phab.mercurial-scm.org/D11691

backout: backed out changeset 2f2107c01dee After discussion on the original phab patch, we've decided to wait until Python 2 support is dropped to do this since the behavior differs for relatively obscure reasons. Differential Revision: https://phab.mercurial-scm.org/D11692

backout: backed out changeset 6edc8800dbc3 Same as the previous changeset. Differential Revision: https://phab.mercurial-scm.org/D11693

dirstate-v2: preserve the fallback values on disk When the fallback values are set, they are now read and written to disk. See format documentation for details. Differential Revision: https://phab.mercurial-scm.org/D11688

dirstate: make DirstateItem constructor accept fallback value This could arguably goes in the previous changeset, but I wanted to keep that previous changeset small to focus more on the user code and the documentation. Differential Revision: https://phab.mercurial-scm.org/D11687

dirstate: add a concept of "fallback" flags to dirstate item The concept is defined and "used" by the flag code, but it is neither persisted nor set anywhere yet. We currently focus on defining the semantic of the attribute. More to come in the next changesets Check the inline documentation for details. Differential Revision: https://phab.mercurial-scm.org/D11686