branchcache: stop storing a repository instance on the cache altogether We did not really needed it and we do not needs it anymore at all. So lets make things simpler for consistency and garbage collecting and stop storing it altogether.

branchcache: pass the target repository when copying Branchmap are usually copied to be used on a different repoview using a different filter level. Passing the repository around means the repository in `branchcache._repo` will drift from the actual branchmap filter. This is currently "fine" because the repo is only used to retrieve the `nullid` value. However, this is a fairly big trap for any extension or future code using the `_repo` attribute. The replace logic is now using a copy to ensure the right repository view is used to initialized the cached value. We add a couple of assert for make sure this inconsistency does not sneak back.

branchcache: have an explicit method to update the on disk cache Explicit is better and will give use more flexibility for future evolution of the storage.

crecord: drop calls to `curses.endwin()` We got a bug report where `curses.endwin()` failed with `_curses.error: endwin() returned ERR`. Looking at e306d552dfb12, it seems like we should be able to just remove these calls.

config: move the option to mmap rev branch cache in the storage section See previous commit for rational.

config: document the storage and format sections This should help people to put configuration in the right section.