isWindow returns true when it should be false

[robinemarr@…]

var x = {};
x.window = x;

$.isWindow(x); // returns true

why not use:

isWindow = function (obj) {
    return obj && obj !== null && obj === window;
}

instead of:

isWindow = function (obj) {
    return obj && obj !== null && obj === obj.window;
  }

[dmethvin]

Duplicate of #12901.