Fixed hanging on windows when there is no manifest

`findroot()` was getting into an infinite loop on windows, because this would never end:

```js
while (!exists(join(path, 'component.json')) && '/' != path) {
  path = dirname(path);
}
```

as windows root is not `/`.

At first I've tried using regexp, but than figured the path splitting approach would be more robust as there might be different path types, like `\\NETWORK\dir` and what not...
When would `sep != 'c:\'` be true?