Clean-up Context#stack.

lib/liquid/context.rb

@@ -86,19 +86,13 @@ module Liquid
     #   end
     #
     #   context['var]  #=> nil
-    def stack(new_scope={},&block)
+    def stack(new_scope={})
-      result = nil
       push(new_scope)
-
+      yield
-      begin
-        result = yield
     ensure
       pop
     end
 
-      result
-    end
-
     def clear_instance_assigns
       @scopes[0] = {}
     end