MFC r305819:
Sync libarchive with vendor including important security fixes.

Issues fixed (FreeBSD):
PR #778: ACL error handling
Issue #745: Symlink check prefix optimization is too aggressive
Issue #746: Hard links with data can evade sandboxing restrictions

This update fixes the vulnerability #3 and vulnerability #4 as reported in
"non-cryptanalytic attacks against FreeBSD update components".
https://gist.github.com/anonymous/e48209b03f1dd9625a992717e7b89c4f

Fix for vulnerability #2 has already been merged in r305192.

Security: http://gist.github.com/anonymous/e48209b03f1dd9625a992717e7b89c4f