some cleanups to opt/loop.c
some cleanups to opt/loop.c

The optimisation still doesn't appear to do anything for me...

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