Automagic annotations for INHERITED

[pipping]

14:22 <pipping> fauxmight: that exheres has `require cairo` in
                it. that works even though there is no
                cairo.exlib in exlibs/ for any of its masters
                or in the repo itself?
14:23 <pipping> ciaranm: ^
14:25 <ciaranm> it should error if there's no exlib found
14:27 <pipping> ciaranm: and under these circumstances no exlib
                should be found because the only exlib of that
                name is x11-libs/cairo/cairo.exlib in ::x11
14:27 <pipping> (which is a master of ::fauxmight but anyway)
14:50 <ciaranm> pipping: hrm. plz2ticket automagic annotations
                for INHERITED saying where it found stuff