fix block initialization

lib/virtual/block.rb

@@ -12,6 +12,7 @@ module Virtual
     def initialize(name , method )
       super()
       @method = method
+      raise "Method is not Method, but #{method.class}" unless method == :dummy or method.is_a?(Parfait::Method)
       @name = name.to_sym
       @branch = nil
       @codes = []