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

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

Remove 'uio' argument from MAC Framework and MAC policy entry points for
extended attribute get/set; in the case of get an uninitialized user
buffer was passed before the EA was retrieved, making it of relatively
little use; the latter was simply unused by any policies.

Obtained from: TrustedBSD Project
Sponsored by: Google, Inc.

The V* flags passed using an accmode_t to the access() and open()
access control checks in mac_bsdextended are not in the same
namespace as the MBI_ flags used in ugidfw policies, so add an
explicit conversion routine to get from one to the other.

Obtained from: TrustedBSD Project

Introduce accmode_t. This is required for NFSv4 ACLs - it will be neccessary
to add more V* constants, and the variables changed by this patch were often
being assigned to mode_t variables, which is 16 bit.

Approved by: rwatson (mentor)

Add TrustedBSD credit to new ugidfw_internal.h file.

Break mac_bsdextended.c out into multiple .c files, with the base access
control logic and policy registration remaining in that file, and access
control checks broken out into other files by class of check.

Obtained from: TrustedBSD Project