Implement missing expression constructs

```
These include:

* Let
* Try-except
* Finally
* For
* While
* Throw
* Return
* Address and dereference expressions
* Sizeof expressions
* Numerical negation and exponentiation
* Boolean-algebra expressions
```

Original issue reported on code.google.com by `eligottlieb@gmail.com` on 27 Apr 2011 at 6:41
