Use a real Dummy node instead of misusing an Unknown node and shortly deactivating CSE.
Use a real Dummy node instead of misusing an Unknown node and shortly deactivating CSE.

[r27002]

MatzeB/libfirm,MatzeB/libfirm,jonashaag/libfirm,8l/libfirm,davidgiven/libfirm,jonashaag/libfirm,jonashaag/libfirm,8l/libfirm,MatzeB/libfirm,killbug2004/libfirm,8l/libfirm,8l/libfirm,davidgiven/libfirm,davidgiven/libfirm,libfirm/libfirm,8l/libfirm,killbug2004/libfirm,davidgiven/libfirm,jonashaag/libfirm,killbug2004/libfirm,libfirm/libfirm,davidgiven/libfirm,jonashaag/libfirm,libfirm/libfirm,davidgiven/libfirm,killbug2004/libfirm,libfirm/libfirm,MatzeB/libfirm,8l/libfirm,8l/libfirm,MatzeB/libfirm,davidgiven/libfirm,killbug2004/libfirm,jonashaag/libfirm,libfirm/libfirm,killbug2004/libfirm,killbug2004/libfirm,MatzeB/libfirm,jonashaag/libfirm,MatzeB/libfirm