Handling of relative proxy uris

[hallvard]

I think I've discovered an issue in proxy uri handling. If there is a relative uri in an emfjson file and the reference.isResolveProxy() is true and type != null the referenced object is not resolved, yet, but instead a proxy object (of the indicated type) is created. This is as it should be. But the proxy uri that is stored in the object is the same relative uri, but I think it should be a resolved absolute uri. If not, it won't resolve correctly later. I took a look at XMLHandler and it seems to resolve the uri against the referencing object's resource uri, before storing it in the proxy.