**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
<li ref={(r) => log.push(r)} />
          </ul>
        </span>
      </div>,
      {createNodeMock, foobar: true},
    );
    ReactTestRenderer.create(
      <Foo />,
      {createNodeMock},
    );
    ReactTestRenderer.create(
      <div ref={(r) => log.push(r)} />,
    );
    ReactTestRenderer.create(
      <div ref={(r) => log.push(r)} />,
      {}
    );
    expect(log).toEqual([
      mockDivInstance,
      mockInputInstance,
      mockListItemInstance,
      mockListItemInstance,
      mockListItemInstance,
      mockAnchorInstance,
      null,
      null,
    ]);
  });
  it('supports unmounting when using refs', () => {
    class Foo extends React.Component {