Improve the AM folding heuristics: Do not fold AM if at least one of the AM operands is not used except for this address calculation.
Improve the AM folding heuristics: Do not fold AM if at least one of the AM operands is not used except for this address calculation.

[r16324]

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