JBCACHE-1412 - Marshaller uses equals() to test object equality instead of identity when performing reference counting

The marshalling logic in TreeCacheMarshaller140 uses a HashMap as store of objects already written so it can replace subsequent writes of the same object with a magic number. Use of a HashMap is incorrect, as magic number replacement should only occur if an object with the same identity is detected, not one that just satisfies equals() but not ==.

See JBCACHE-1412.