using bus_alloc_resource(), etc., are especially unobvious, but were
especially wrong (<sys/resource.h> has nothing to do with the resources
documented here...). Order and format the includes as correctly as
possible (a layering violation makes <machine/bus.h> a prerequisite for
<sys/rman.h>).
bus_release_resource.9 contains a paragraph obtained from a mail
by Warner Losh <imp@FreeBSD.org> to myself.
Reviewed by: asmodai, hoek; in parts by msmith, mdodd and imp