added comments documenting the new behavior of get_nodes_block(). typos fixed
added comments documenting the new behavior of get_nodes_block().
typos fixed

[r6140]

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