Path.set_unreadable_for_all instead of Path.set_readable_for_all(false) (and r/w/x, all/owner)
Add these functions.
Since it is not good to pass "false" to set_xxxable_for_xxx. In those cases, the meaning of "false" is not clear for readers who does not know the spec of the functions. For example, readers might think "false" means "not recursively."