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

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

Handle NULL return from crypt(3). Mostly from DragonFly

Fix fd leak

MFC after: 3 days

Use strchr() instead of index(). Use getopt(). Use err().

ANSIify function definitions to avoid some warnings.
Include stdlib.h for exit.

Style improvements recommended by Bruce as a follow up to some
of the recent WARNS commits. The idea is:

1) FreeBSD id tags should follow vendor tags.
2) Vendor tags should not be compiled (though copyrights probably should).
3) There should be no blank line between including cdefs and __FBSDIF.

WARNS=2 fixes. Also, use __FBSDID(), and sort includes.

This commit was generated by cvs2svn to compensate for changes in r26240,
which included commits to RCS files with non-trunk default branches.

Import chkey.

This program is used to change a user's existing public and secret key pair.