make machine init default to the running one with ruby config

lib/vm/program.rb

@@ -20,8 +20,11 @@ module Vm
     
     # Initialize with a string for cpu. Naming conventions are: for Machine XXX there exists a module XXX
     #  with a XXXMachine in it that derives from Vm::Machine
-    def initialize machine
+    def initialize machine = nil
       super("start")
+      machine = RbConfig::CONFIG["host_cpu"] unless machine
+      machine = "intel" if machine == "x86_64"
+      machine = machine.capitalize
       Machine.instance = eval("#{machine}::#{machine}Machine").new
       @context = Context.new(self)
       #global objects (data)