fixed fc_val_from_str() do NOT produce values with more significant bits than requested in the mode
fixed fc_val_from_str() do NOT produce values with more significant bits than requested in the mode

[r15236]

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