Hello guys, Just a heads up, I bumped packagekit to recent release and had to upgrade packagekit-qt4 while doing so. It appears that while added support for qt5 (not in tree right now) but it broke the way kcm-grub2 autodetects packagekit-qt4. Since packagekit-qt4 provides a nice pkgconfig file so I guess patching the custom cmake wouldn't be to hard for you.
Dependency restricted for now. I doubt that there is any gentoo kde project maintainer still on Plasma 4. Please feel free to re-open if you want to work on it. https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=d9fb7c1085d697c06136051e8a93736d903e6513
