Unusable header fix-ups

IOhannes m zmoelnig reported (via https://bugs.debian.org/761191) that a few
headers are missing the leading / in their boilerplate, which renders them
unusable. The attached patch (against master) fixes this; it applies to
stable too.

Patch by Stephen Kitt -- skitt at debian.org
(cherry picked from commit 41cdb6e73edebdab1d568ed6dde0672861026331)