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

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

Typedefing an array of incomplete structs is non-standard C code.

Approved by: das (mentor)

Implement this (quoted from the updated man page): If the first token
of a rule specification is a single dash (``-''), rules are read from
the standard input and the rest of the specification is ignored.

Introduce the DEVFS "rule" subsystem. DEVFS rules permit the
administrator to define certain properties of new devfs nodes before
they become visible to the userland. Both static (e.g., /dev/speaker)
and dynamic (e.g., /dev/bpf*, some removable devices) nodes are
supported. Each DEVFS mount may have a different ruleset assigned to
it, permitting different policies to be implemented for things like
jails.

Approved by: phk