DATAMONGO-1086 - Mapping fails for collection with two embbeded types that extend a generic abstract.

Prepare issue branch.
DATAMONGO-1086 - Mapping fails for collection with two embbeded types that extend a generic abstract.

We now use the type information of the raw property type to check if we need to include _class.
DATAMONGO-1100 - Upgrade to new PersistentPropertyAccessor API.