This review adds acl_from_mode_np, acl_cmp_np and acl_equiv_mode_np functions.
These functions without _np prefix are present in Linux libacl and some software
(KDE, specifically) uses them along with standard POSIX ACL functions.
It is impossible to implement some of them outside of libc, and since we already
have a bit of *_np functions, I decided to implement these.