forgetObject
is called when the objects finalize() is called, if
it's opid is still valid. If all data were local, this would mean the object
could be desroyed because it's not reachable anymore. But because more
references may exist at the servers end, this basically reduces the reference
count at the servers side.
Server side garbage collection will eventually reclaim the object space, if
it really has become unreachable.
The function adjusts the cache manager's cache size and links the object into the
forgottenObjectList of the cache manager