cext: add support for revlogv2 This enables the C code to retrieve/create entries in the revlog v2 format. This is mainly a matter of taking into account the additional slots for sidedata, etc. Differential Revision: https://phab.mercurial-scm.org/D9846

bitmanipulation: add utils to read/write bigendian 64bit integers Differential Revision: https://phab.mercurial-scm.org/D9845

format: remove sidedata format variant This format variant can only exist when also using revlog v2, so it's useless now. Differential Revision: https://phab.mercurial-scm.org/D10113

revlogv2: allow upgrading to v2 Revlogv2 implies sidedata. Right now sidedata is not really used in production, and Revlogv2 will be used for the first production-ready version of sidedata support. Differential Revision: https://phab.mercurial-scm.org/D9844

revlog: introduce v2 format As documented in [1], this is still tentative and could be subject to change, but we need to lay down the foundations in order to work on the next abstraction layers. [1] https://www.mercurial-scm.org/wiki/RevlogV2Plan Differential Revision: https://phab.mercurial-scm.org/D9843

formatting: fix redundant parentheses These were introduced by 0d055849d5f9d682ef931d2566b760d5c6bf7e52. Differential Revision: https://phab.mercurial-scm.org/D10229