externalizable classes fail with custom readClassDescriptor/writeClassDescriptor

This is a follow-on to bug 4461299. Employing the fix described in that bug to Merlin build 65 allows Weblogic to proceed to a later point in its initialization, but the initialization still ultimately fails. It is now failing due to a StreamCorruptedException that is thrown when it tries to read an externalizable object. I have attached a small test case. Triggering the bug still requires the custom readClassDescriptor/writeClassDescriptor methods, and it requires that the externalizable class write some non-standard data in its writeExternal method (such as the boolean value that the test case writes); that follows the Weblogic model.