Make sure we do the child key warning for all cases

[zpao]

This should warn but doesn't

var f = <span/>
var g = <span/>

var children = [f, g];

return (
  <div>
    <div key="0">
      {g}
    </div>
    <div key="1">
      {f}
    </div>
    <div key="2">
      {children}
    </div>
  </div>
);

Turns out we're modifying f and g after the first time to set ._store.validated and then not looking again if already validated.

[sophiebits]

Keep in mind that

var Wrapper = React.createClass({
  render: function() {
    return <div>
      {this.props.children}
      <Footer />
    </div>;
  }
});

React.render(
  <Wrapper>
    <A />
    <B />
  </Wrapper>,
  document.body
);

shouldn't warn.