allow general conversions between reference and interegr modes
allow general conversions between reference and interegr modes

[r15658]

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