I made a mistake caught by code review earlier, so let's try to be
safer by default.
This patch also moves all our "forwarding" headers to the guardless
just-include-the-other-thing style that we usually use. (Where we
have a comment explaining where the header comes from, I've kept
that.)
Change-Id: I37342cf5e2563c6a269b2ba61a697069b1c7913b