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

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

It seems the pre-commit checker doesn't detect illegal character sets. Fix.

Give up on using iconv to convert to UTF-8 at build time. I don't see any
practical way to make iconv(1) as a build tool. Instead pre-convert.
This gives us UTF-8 nvi catalogs even on systems without iconv enabled.