manifest: apply checkambig=True only for root 00manifest.i This is a fix for my 14ad8e2a4abe, which used 'bool(dir)' as checkambig value for revlog.__init__(). I can't remember why I did so in 14ad8e2a4abe, but this is obviously wrong, because only root indexfile is cached via filecache-ed property of localrepository.