**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
return null;
    }
    var renderer = ReactTestRenderer.create(<Empty />);
    expect(renderer.toJSON()).toEqual(null);
  });
  it('exposes a type flag', () => {
    function Link() {
      return <a role="link" />;
    }
    var renderer = ReactTestRenderer.create(<Link />);
    var object = renderer.toJSON();
    expect(object.$$typeof).toBe(Symbol.for('react.test.json'));
    
    for (var key in object) {
      if (Object.prototype.hasOwnProperty.call(object, key)) {
        expect(key).not.toBe('$$typeof');
      }
    }
  });
  it('renders some basics with an update', () => {
    var renders = 0;
    class Component extends React.Component {