simplify and maybe even fix bugs in turn_into_tuple
simplify and maybe even fix bugs in turn_into_tuple

[r27672]

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