[kde-frameworks/kcoreaddons] Specify KDE4 home prefix.

This is required because kdelibs:4 was built with -DKDE_DEFAULT_HOME=.kde4
and Kdelibs4Migration no longer autodetects the directory name.

Upstream commit: d36771ebfc6e8a3bbeafb42be0580cfc6e8f2daf

Package-Manager: portage-2.2.12