Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

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Approved by: jedgar

Improve ACL branding mismatch detection and reporting in some rare cases,
such as "setfacl -m ''".

Add NFSv4 support to setfacl(1).

Reviewed by: rwatson

/*- or .\"- or #- to begin license clauses.

Consistently use FBSDID

Add defines for access and default ACLs (ACCESS_ACL/DEFAULT_ACL)
to enhance readability.

Obtained from: TrustedBSD Project

style(9) cleanups mostly consisting of:
o explicitly check return values and variables against a value
o return x; -> return (x);
o fix inconsistent sysexits usage by nuking it (partially
suggested by bde)

Obtained from: TrustedBSD Project

o Separate acl_t into internal and external representations as
required by POSIX.1e. This maintains the current 'struct acl'
in the kernel while providing the generic external acl_t
interface required to complete the ACL editing library.
o Add the acl_get_entry() function.
o Convert the existing ACL utilities, getfacl and setfacl, to
fully make use of the ACL editing library.

Obtained from: TrustedBSD Project

o POSIX.2c Userland tool support for POSIX.1e ACLs -- getfacl retrieves ACLs
from files and directories, and setfacl sets ACLs on files and directories.

Submitted by: jedgar
Obtained from: TrustedBSD Project