**Do you want to request a *feature* or report a *bug*?**

bug

**What is the current behavior?**

componentWillUnmount for inner instances is never called.

Here are 2 (jest) tests, the first works, not the second.

```js
import React from "react";
import renderer from "react-test-renderer";

test("top level componentWillUnmount works", () => {
  let count = 0;
  class A extends React.Component {
    componentWillUnmount() {
      count ++;
    }
    render() {
      return <div />;
    }
  }
  const inst = renderer.create(<A />);
  inst.unmount();
  expect(count).toEqual(1);
});

test("inner componentWillUnmount works", () => {
  let count = 0;
  class A extends React.Component {
    componentWillUnmount() {
      count ++;
    }
    render() {
      return <div />;
    }
  }
  const inst = renderer.create(
    <div>
      <A />
    </div>
  );
  inst.unmount();
  expect(count).toEqual(1);
});
```

**What is the expected behavior?**

The two test above should pass. All component that are unmounted should have the proper lifecycle, whatever the nesting is.

**Which versions of React, and which browser / OS are affected by this issue? Did this work in previous versions of React?**

React 15.4.0
log.push('mount ' + this.props.name);
      }
      componentWillUnmount() {
        log.push('unmount ' + this.props.name);
      }
    }
    var renderer = ReactTestRenderer.create(<Log key="foo" name="Foo" />);
    renderer.update(<Log key="bar" name="Bar" />);
    renderer.unmount();
    expect(log).toEqual([
      'render Foo',
      'mount Foo',
      'unmount Foo',
      'render Bar',
      'mount Bar',
      'unmount Bar',
    ]);
  });
  it('gives a ref to native components', () => {
    var log = [];
    ReactTestRenderer.create(<div ref={(r) => log.push(r)} />);
    expect(log).toEqual([null]);
  });
  it('warns correctly for refs on SFCs', () => {
    spyOn(console, 'error');
    function Bar() {
      return <div>Hello, world</div>;
    }
    class Foo extends React.Component {