MFC r300903: Implement SHA-512 truncated (224 and 256 bits)

MFC r292782: 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

Approved by: secteam

MFC r282726: Ensure libmd symbols do not clash with libcrypto

Add a prefix to all symbols in libmd to avoid incompatibilites
with same-named, but not binary compatible, symbols from libcrypto.

Also introduce Weak aliases to avoid the need to rebuild dependent
binaries and a major version bump.

PR: 199119

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

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

Add SHA512 (Actually, this is Colin Percival's code for SHA256, with
relevant constants changed).

While I'm here clean up the tests and Makefile.

PR: misc/124164
Submitted by: KIMURA Yasuhiro < yasu utahime org >
MFC after: 1 month

In light of the recent 2^69 operation collision-finding attack on SHA1,
add support for SHA256.

Tested on: i386, sparc64
Tested using: NIST test vectors, built-in tests
X-MFC-after: 5.4-RELEASE

add __FBSDID()s to libmd

$Id$ -> $FreeBSD$

Fix bug in MDx test suite.
Add Eric Young's SHA-[01] implementations.