fixed indent removed dependency on current_ir_graph in exchange() added som asserts in exchange()
fixed indent
removed dependency on current_ir_graph in exchange()
added som asserts in exchange()

[r8653]

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