cperciva's libmd implementation is 5-30% faster (also seen here: https://svnweb.freebsd.org/changeset/base/r263218 )
cperciva's implementation was lacking SHA-384 which I implemented
Extend sbin/md5 to create sha384(1)
In a separate commit, I will also add SHA-512/256 (required by new ZFS features)
Chase dependancies on sys/crypto/sha2/sha2.{c,h} and replace them with sha512{c.c,.h}
Will extend reviewers to include secteam@ once the first round of issues are dealt with