Contexts still can't see outer scope. Add failing test.

examples/nested_context.py

@@ -3,5 +3,8 @@ import pystache
 class NestedContext(pystache.View):
     template_path = 'examples'
 
+    def outer_thing(self):
+        return "two"
+
     def foo(self):
         return {'thing1': 'one', 'thing2': 'foo'}