Updated objects should not be rewritten in WriteTransaction

When listening to changes in DS, "put" creates/replaces data. When changing properties of an object in WriteTransaction by using "put", various listener implementations expect data modification and not creation/replacement.

E.g. when a class implements listening to changes in DS by extending DataTreeChangeListener, modification type WRITE is received when modifying existing data in transactions by "put". However, by using "merge" received modification type is SUBTREE_MODIFIED, which is a proper consequence.