nodemap: write nodemap data on disk Let us start writing data on disk (so that we can read it from there later). This series of changeset is going to focus first on having data on disk and updating it. Right now the data is written right next to the revlog data, in the store. We might move it to cache (with proper cache validation mechanism) later, but for now revlog have a storevfs instance and it is simpler to us it. The right location for this data is not the focus of this series. Differential Revision: https://phab.mercurial-scm.org/D7835

nodemap: have some python code writing a nodemap in persistent binary form This python code aims to be as "simple" as possible. It is a reference implementation of the data we are going to write on disk (and possibly, later a way for pure python install to make sure the on disk data are up to date). It is not optimized for performance and rebuild the full data structure from the index every time. This is a stepping stone toward a persistent nodemap on disk. Differential Revision: https://phab.mercurial-scm.org/D7834