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

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

Replace our (un)vis(1) commands with implementations from NetBSD to
match our import of the (un)vis(3) APIs.

This adds support for multibyte encoding and the -h and -m flags which
support HTTP and MIME encoding respectively.

PR: bin/175418
Obtained from: NetBSD

WARNS=2 is going to become the default, so remove it from here.

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 cleanups. Add FreeBSD ID to Makefile.

This commit was generated by cvs2svn to compensate for changes in r1590,
which included commits to RCS files with non-trunk default branches.

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