I167 - NPE when when Entity has @GeneratedValue(strategy = GenerationType.IDENTITY) id and @version

First commit :
-TestCase

The fix can be split in 2 part :
-One : Made the hashCode of ManagedInstance null safe about the id.
-Two : Change the implementation of Set of changedEntities in SessionImpl to an "IdentityHashSet", this prevent early time hashCode computation which would be based on EntityName without the Id, causing the immutable value of hashCode to have bad dispersion.