add 2.0*x = x+x and x/c = x*(1.0/c) for some constants
add 2.0*x = x+x and x/c = x*(1.0/c) for some constants

[r15327]

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