Fixed dca transfer function for Add, Sub, Minus, Mul and Shl.
Fixed dca transfer function for Add, Sub, Minus, Mul and Shl.

We have to consider that less significant bits of the operands
can affect more significant bits of the operation itself.

This fixes opt/occult2.c and 177.mesa.

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