dillon1000/react

Inputs should not mutate value on type conversion (#9806)

This is a follow-up on
https://github.com/facebook/react/pull/9584#discussion_r115642293. There
is no need to assign the value property of an input if the value
property of the React component changes types, but stringifies to the
same value. For example:

```javascript
DOM.render(<input value="true" />, el)
DOM.render(<input value={true} />, el)
```

In this case, the assignment to `input.value` will always be
cast to the string "true". There is no need to perform this
assignment. Particularly when we already cast the value to a string
later:

```javascript
// Cast `value` to a string to ensure the value is set correctly. While
// browsers typically do this as necessary, jsdom doesn't.
node.value = '' + value;
```