jumpthreading must not split edges
jumpthreading must not split edges

* the splitted edge is never critical, so the name was misleading
* it might result in an infinite loop
  fixes opt/jumpthreading5 and opt/jumpthreading5b

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