Add NFSv4 ACL support for Mac OS X

Add NFSv4 ACL support for Mac OS X

Mac OS X supports user and group NFSv4-style ACLs only (extended ACLs).
File-mode ACLs (owner@, group@ and everyone@) are not supported.

Behavior on Mac OS X:
- libarchive does not store GUID of Mac OS X extended ACLs. Only
  uid or gid (and the corresponding user or group name) are stored.
- When extracting an archive entry that has mac_metadata, NFSv4 ACLs
  are not written to disk (mac_metadata already contains ACLs)
- When writing ACLs to disk from an archive entry with NFSv4 ACLs
  owner@, group@ and everyone@ ACLs are ignored. User and group ids
  are converted to a GUID (this may lead to a fabricated GUID if
  the user or group ID is not present on the system)
- When reading ACL from disk and there is at least one user or group
  extended ACL entry, owner@, group@ and everyone@ entries mirroring
  the file mode are added to the end of the entry's ACL.