revlog: directly use self._format_version when loading index The shorthand variable does not bring much, so we drop it to simplify the code. Differential Revision: https://phab.mercurial-scm.org/D10599

revlog: use `_format_flags` to access flags instead of `header` It seems better to reuse the variable we carefully extracted This also open the way to more flexible way to retrieve these flags. Differential Revision: https://phab.mercurial-scm.org/D10598

revlog: rename `newversionflags` to `new_header` This make it consistent with the previous changeset. Differential Revision: https://phab.mercurial-scm.org/D10597

revlog: rename `versionflags` to header The variable is named as such because it contains "version" information and "flags" information. However you mostly needs to know the code to understand the name which is not great. The fact that this is the very first four bytes in all revlog seems more relevant, so we rename the variable "header". Differential Revision: https://phab.mercurial-scm.org/D10596

revlog: move index reading logic in a dedicated method They are multiple motivation to do it: * The logic is complicated enough to deserver its own method. * We will need to reuse this once we put a docket in use. * This split the actual reading from the processing of the read data better. Differential Revision: https://phab.mercurial-scm.org/D10595

revlog: define the actual index and datafile at loading time This is just code movement, to make the code closer to where we actually use it and where it will be defined in the future. Differential Revision: https://phab.mercurial-scm.org/D10594

revlog: simplify a conditionnal in _enforceinlinesize This is a gratuitous change to make things a bit easier to read. Differential Revision: https://phab.mercurial-scm.org/D10593

revlog: drop `flush` parameter from `_peek_iscensored` This is not used anywhere. Differential Revision: https://phab.mercurial-scm.org/D10592

revlog: fix error message when data are missing The error message the message was not using the requested offset, but the adjusted offset to that read more data for improved caching. This resulted in confusing error message. Differential Revision: https://phab.mercurial-scm.org/D10591

revlog: rename `nodemap_file` to `_nodemap_file` Same reasoning as for `indexfile and datafile`, lets hide these implementation details. Differential Revision: https://phab.mercurial-scm.org/D10590