xattr and ACL support for Solaris 11 and OpenIndiana

xattrs: Solaris 11 and OpenIndiana have the same API (O_XATTR):
- https://illumos.org/man/5/fsattr
- http://docs.oracle.com/cd/E23824_01/html/821-1474/fsattr-5.html

Note that xattr/fsattr in sunos5 is far more powerful than on the other platforms. On sunos5 they are essentially file system namespace attached to every file. You can put any file type in there (e.g. sockets, block devices, link) and have arbitrarily complex directory structures. So it may make sense to map these into normal items (NUL as separator? - other platforms would not extract) and traverse them. Or, we could flatten them and only regard regular files (i.e. key-value pairs).

ACLs: APIs are also similar to each other (and our already implemented APIs)
- http://docs.oracle.com/cd/E23824_01/html/821-1474/acl-5.html
- https://illumos.org/man/5/acl