failing test case for for-of loops

It seems that while the `for-in` statement is supported the `for-of` statement is not. According to the [latest draft spec](http://people.mozilla.org/~jorendorff/es6-draft.html#sec-runtime-semantics-forin-div-ofbodyevaluation) `for-in` and `for-of` work the same (or so goes my reading, which may be wrong!).

Anyway here's a test case for the `for-of` statement but the emitter currently fails as it doesn't understand the `for-of` statement.