RealmResult iterators now detect changes to underlying tableview.

RealmResults now correctly identify any changes to the underlying query tableview and throws a ConcurrentModificationException if detected.

@kneth @bmunkholm @emanuelez 
We don't catch exceptions in this method in other JNI calls, Also we wouldn't be able to handle it very well? We could perhaps return -1, but isn't it better to just have the exception?

I will add the cast.