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

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

Add SHA256/512 ($5$ and $6$) to crypt(3). Used in linux-world, doesn't
hurt us.

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

No functional change, but big code cleanup. WARNS, lint(1) and style(9).

Implement __FBSDID()

Big code cleanup. (Inspired by Brandon Gillespie). Also move as
much as possible away from secure/ to make extending easier.