Let edges_assure() only activate edge kinds, which are not activated yet.
Let edges_assure() only activate edge kinds, which are not activated yet.

[r23176]

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