sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

Fix C++ includability of crypto headers with static array sizes

C99 allows array function parameters to use the static keyword for their
sizes. This tells the compiler that the parameter will have at least the
specified size, and calling code will fail to compile if that guarantee is
not met. However, this syntax is not legal in C++.

This commit reverts r300824, which worked around the problem for
sys/sys/md5.h only, and introduces a new macro: min_size(). min_size(x) can
be used in headers as a static array size, but will still compile in C++
mode.

Reviewed by: cem, ed
MFC after: 4 weeks
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D8277

libmd: introduce functions that operate on an fd instead of filename

Reviewed by: allanjude, cem
MFC after: 2 months
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D8264

crypto routines: Hint minimum buffer sizes to the compiler

Use the C99 'static' keyword to hint to the compiler IVs and output digest
sizes. The keyword informs the compiler of the minimum valid size for a given
array. Obviously not every pointer can be validated (i.e., the compiler can
produce false negative but not false positive reports).

No functional change. No ABI change.

Sponsored by: EMC / Isilon Storage Division

Replace sys/crypto/sha2/sha2.c with lib/libmd/sha512c.c

cperciva's libmd implementation is 5-30% faster

The same was done for SHA256 previously in r263218

cperciva's implementation was lacking SHA-384 which I implemented, validated against OpenSSL and the NIST documentation

Extend sbin/md5 to create sha384(1)

Chase dependancies on sys/crypto/sha2/sha2.{c,h} and replace them with sha512{c.c,.h}

Reviewed by: cperciva, des, delphij
Approved by: secteam, bapt (mentor)
MFC after: 2 weeks
Sponsored by: ScaleEngine Inc.
Differential Revision: https://reviews.freebsd.org/D3929