Fix the remaining case in issue #4

An original function (a function that was in the original code) should be transformed separately from the code it's in. If the outside code uses try/catch, neither the function, _nor the continuations that are generated inside it_, should be affected. (Tell me if I should go into more detail. It might not be clear this is correct.)

This builds on your work made in 7e2627e4ea8110ce36e72ab3d8fdf999d00a08bb to fix [my modified test case](https://github.com/BYVoid/continuation/issues/4#issuecomment-14977935) and also adds that as a new unit test.

Note: Though `traverse()` is also used elsewhere, notably in WhileStatement and SwitchStatement, and they don't use `currentScope: true`, I wasn't able to find a bug analogous to #4 for them. I think those `traverse()` calls don't need changing.