Recommendation for CompatibleFieldSerializer

I read the example in #643, and I see that in @NathanSweet last comment says when decode `SomeClass#anotherClass` but `AnotherClass`'s structure is missing, it will cause decode failure. Because `CompatibleFieldSerializer` serialize is great depandency in order. When reading, the `AnotherClass` class doesn't exist, Kryo will skip `AnotherClass` 's chunked input buffer.
See `CompatibleFieldSerializer#read`'s `readUnknownTagData` part down below.

```
Registration registration;
try {
registration = kryo.readClass(fieldInput);
} catch (KryoException ex) {
if (!chunked)
throw new KryoException("Unable to read unknown data (unknown type). (" + getType().getName() + ")", ex);
if (DEBUG) debug("kryo", "Unable to read unknown data (unknown type).", ex);
inputChunked.nextChunk();
continue;
}
```

But the information of `SomeClass#value` is still int that buffer, so if we continue read the remaing buffer that we can cache the `SomeClass#value` in `SomeClass#anotherClass`'s chunked input.
So I simply do that:
```
Registration registration;
try {
registration = kryo.readClass(fieldInput);
} catch (KryoException ex) {
if (!chunked)
throw new KryoException("Unable to read unknown data (unknown type). (" + getType().getName() + ")", ex);
if (DEBUG) debug("kryo", "Unable to read unknown data (unknown type).", ex);
//inputChunked.nextChunk();
//continue;
registration = kryo.getRegistration(Object.class);
}
```

If Kryo can't find the Class so we give it a default Class that has no field in it, then Kryo successfully read the remaing byte in buffer and cache the `SomeClass#value` in `SomeClass#anotherClass`'s chunked input.

This change is usefull in my case, but I don't know it will have impact for other case? Or you consider add this change (maybe with configurable) in futrue release?

Looking forward to your reply.