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

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

Flesh out WITHOUT_GROFF support to DTRT.

A full featured groff is required during buildworld, so build it always
and don't rely on it being present on the host system.

vgrind(1) is tightly coupled to a roff processor and will not be
built/installed when groff is disabled. Also much of the roff'ed
documentation under share/doc will not be built/installed when
WITHOUT_GROFF is defined.

Reviewed by: ru (partial)

Prepare to autogenerate the src.conf(5) manpage.