Support for ember-1.0.0-rc.3

The commit [c28f05af](https://github.com/emberjs/ember.js/commit/c2c483dc592bb926c210e2c4c174dba7314d18dd#L0R128) replaced `window.history.replaceState(...)` with `get(this, 'history').replaceState(...)`. So we need to set the `history` attribute before calling `@replaceState` in `initState`.

I haven't written any tests, but it's working fine in my (in-house) app.