Event serializer has side effects that change the underlying Event data

[rianjs]

Stick this in SerializationTests:

[Test]
public void DurationIsStable_Tests()
{
    var e = GetSimpleEvent();
    var originalDuration = e.Duration;
    var c = new Calendar();
    c.Events.Add(e);
    SerializeToString(c);
    Assert.AreEqual(originalDuration, e.Duration);
}

[rianjs]

38165f8