def executable?
      self.class.recipes.each do |meth,args|
        return false unless respond_to?(meth)
      end
      return false if executed?
      true
    end
def executable?
      self.class.recipes.each do |meth,args|
        return false unless respond_to?(meth)
      end
      return false if executed?
      true
    end
Returns true if this Manifest <tt>respond_to?</tt> all methods named by
 calls to recipe, and if this Manifest has not been executed before.