restructured reassociation to handle more cases (rule R7, R8 were not working)
restructured reassociation to handle more cases (rule R7, R8 were not working)

[r15531]

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