Default sandbox: useFakeXMLHttpRequest is not restored correctly

[ifrost]

Describe the bug
sinon.useFakeXMLHttpRequest() replaces global XMLHttpRequest object, but it doesn't restore it when sinon.restore() is called. The problem is that sinon object overrides useFakeXMLHttpRequest method instead of using the one from Sandbox class and the fake is not added to the collection that is being restored when sinon.restore() is called.

To Reproduce

it("should restore XMLHttpRequest and ActiveXObject", function () {
    var globalXHR = global.XMLHttpRequest;
    var globalAXO = global.ActiveXObject;
    sinon.useFakeXMLHttpRequest();

    sinon.restore();

    assert.same(global.XMLHttpRequest, globalXHR);
    assert.same(global.ActiveXObject, globalAXO);
});

Expected behavior
The test above should pass.

Context (please complete the following information):

• Library version: 6.0.0
• Environment: OSX, node 8.10.0

[mroderick]

This was fixed with #1841 and published to NPM as sinon@6.1.1