[xstream-user] Make UUID an Immutable type by default

[Geoff Groos]

Hey guys,

We’re just about to go to version 1.0, so I’m running over every piece of 
tech-debt I can think of to make sure all my ducks are in a row, and I found 
this in our project file (an XML serialized model):

      <ProjectState.ImmutableMomento>
        <associatedRunId>b723fec2-50f9-45fa-9a41-fee8d022b544</associatedRunId>
        <!-- ... -->
      </ProjectState.ImmutableMomento>
      <ProjectState.ImmutableMomento>
        <associatedRunId 
reference="../../ProjectState.ImmutableMomento/associatedRunId"/>

I cant think of a good reason for a UUID not to be immutable by default. Doing 
oneID == anotherID has to be as taboo as aString == anotherString to anybody 
whose willing to use a UUID object, meaning I don't think there’s any reason to 
preserve reference equality in serialization.

-Geoff