remove propagation of Unknown. This causes problems in backends in in Firm "hand" construction
remove propagation of Unknown. This causes problems in backends in in
Firm "hand" construction

[r7523]

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