fix old bug in irmemory: external_allocated stuff is also using_unknown
fix old bug in irmemory: external_allocated stuff is also using_unknown

[r22154]

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