More cleanup work on permissions restore:
* Rename some variables/functions/etc to try to make things clearer.
* Add separate flags to control fflag/acl restore
* Collect metadata restore into a single function for clarity
* Propagate errors in metadata restore back out to the client
* Fix some places where errors were being returned when they
shouldn't and vice-versa
* Modes are now always restored; ARCHIVE_EXTRACT_PERM just controls
whether or not umask is obeyed.
* Restore suid/sgid bits only if user/group matches archive
* Cache the last stat results to try to reduce the number of stat calls