`window.__DEV__` should not be compiled to `window.true`

This throws a syntax error in IE8.

`build/modules/utils/__tests__/ImmutableObject-test.js:62`

``` javascript
  var testProd = function(message, testFunc) {
    // Temporarily enter production mode
    window.true = false;
    it(message, testFunc);
    window.true = true;
  };
```

I'm not sure which code is doing this transformation, but this is clearly not what should be happening.
