rev-branch-cache: disable mmapping by default on Windows See the inline comment for why. The commands work, other than leaving extra files laying around. Perhaps there's some way to get this to work like on posix with some `CreateFile` magic (though it already uses `FILE_SHARE_DELETE`, so I'm not sure offhand what else we can do). However big picture- it seems wrong that the old file is left mmapped, a new one moved into place, and the mapping left over the old file instead of retargeted to the new file. That's got to be a bug on posix too, in a long running process like chg, right? If the memory is read again for some reason, it will be stale data.