display help message for illegal command instead of hanging in an inf…

…inite loop

configure

@@ -12,7 +12,7 @@ while [ $# -gt 0 ]; do
 	        prefix="$2"
 	        shift 2
 	    ;;
-        --help)
+        *)
 	        echo 'usage: ./configure [options]'
 	        echo 'options:'
 	        echo '  --prefix=<path>: installation prefix'