Serialization of MemberBox with a delegate is broken

[szegedi]

Serialization of MemberBox with a non-null delegateTo field is broken: the field is declared transient, but never restored upon deserialization. This results in incorrectly deserialized objects.

It can be fixed in two ways:

1. fail early: throw an exception from writeObject if serialization is attempted with a non-null delegateTo.
2. make it work: make the field non-transient.

Now, it's only NativeError that uses the delegate mechanism, and is typically setting it to otherwise serializable values. It seems to me that making the field non-transient is harmless. It was originally made transient in d357f56 11 years ago by @norrisboyd; not sure why – possibly due to a mistake?

Note that making it non-transient will change the serialization format of MemberBox, though.