blackbox: just try writing to repo.vfs and update lastlogger on success This is simpler and more robust. Before, an empty ".hg" directory would be created if it's removed after checking vfs.isdir('.').

vfs: add option to not create parent directories implicitly In blackbox, we don't want to create a ".hg" directory by mistake. This provides a race-safe option to achieve that.

repo: add a `wcachevfs` to access the `.hg/wcache/` directory This wvfs will allow us to migrate various cache to the new `wcache` directory. Helping with cache issues with "share".

cache: create `wcache` directory at init time The cache directory will be needed very quickly, so it seems simpler to create it early to make sure it has the same owner and permission than the other directory in the repository.