Improve additional KDE4 SC directories handling.
Now we have FLAVORs for all supported KDE SC versions. Thus you can:

  cd ${PORTSDIR}/devel/kdevelop && FLAVOR=kde4102 make

Now, our := depends hack can go, but first existing stuff needs to be
converted to use ${MODKDE4_DEP_DIR} instead of hardcoding x11/kde4.