support :focus pseudo selector in mount

[chenesan]

Fixes #1709 by compare document.activeElement and host DOM node of rst node. Work with DOMElement and component element.

Note that this only works with mount, not works with shallow. Also it won't work with simulate:

const wrapper = mount(<input type="text" />)
wrapper.simulate('focus')
// will print false
console.log(wrapper.is(":focus"))

I've tested this with jsdom@6 (in test suite), 13 and 12.

[chenesan]

I didn't know that stateless component not work in react@0.13 so removed it here and rewrite other tests with class component

[malouro]

This hasn't been released yet, right? Curious to know when the next release might be. Thanks 🙂

[ljharb]

@malouro it has been released now, in v3.9.