MFC r316341, r317779, r319071, r319077, r319557, r319558, r319827, r319829:

ext2fs: add read-write support for Extended Attributes and linux ACLs.

Extended attributes and their particular implementation in linux are
different from FreeBSD so in this case we have started diverging from
the UFS EA implementation, which would be the natural reference.

Support for linux ext2fs posix-draft ACLs.

Submitted by: Fedor Uporov
Reviewed by: pfg
Include fixes from: cem, pluknet