test_scope
1. simple nesting
2. extra nesting
3. simple nesting + rebinding
4. nesting with global but no free
5. nesting through class
6. nesting plus free ref to global
7. nearest enclosing scope
8. mixed freevars and cellvars
9. free variable in method
10. recursion
11. unoptimized namespaces
12. lambdas
13. UnboundLocal
