Message 77159 - Python tracker

I think I may have been merging add_ast_fields when I wrote the patch.

Here's a new patch that handles "global x, = (5,)". To do it, I added a
new flag* to the Global and Nonlocal AST objects that indicates whether
the value needs to be unpacked or not.

* The flag is an int. The bool AST type was removed in py3k.