Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

Fix an 11 year old mistake: Let the hash functions take a void* instead
of unsigned char* argument.

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