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
14. complex definitions
15. scope of global statements
16. check leaks
17. class and global
18. verify that locals() works