Remove logical impossibility: A node cannot be a Perm and a Proj at the same time.  Even then the code makes no sense, because setting the proj no of a Proj and exchanging it right after that is pretty pointless.
Remove logical impossibility: A node cannot be a Perm and a Proj at the same time.  Even then the code makes no sense, because setting the proj no of a Proj and exchanging it right after that is pretty pointless.

[r22800]

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