Set old/new from benchmark script args

benchmark/http_simple.js

@@ -1,7 +1,8 @@
 path = require("path");
 
 var puts = require("sys").puts;
-var old = false;
+
+var old = (process.argv[2] == 'old');
 
 http = require(old ? "http_old" : 'http');
 if (old) puts('old version');