title: Can't set layout size in Kivy
body: <p>First of all, if they are some system differences, I work on Ubuntu 12.04, using current Kivy version. My problem is that i'm unable to set layout size.</p>
  
  <pre><code>from kivy.app import App
  from kivy.uix.button import Button
  from kivy.uix.boxlayout import BoxLayout
  
  class TestApp(App):
      def build(self):
          layout = BoxLayout(orientation='vertical', size=(200,200))
          btn1 = Button(text='Hello', size=(50,50), size_hint=(None, None))
          btn2 = Button(text='World', size=(50,50), size_hint=(None, None))
          layout.add_widget(btn1)
          layout.add_widget(btn2)
          return layout
  TestApp().run()
  </code></pre>
  
  <p>Any idea?</p>