Improvement of JPA translator join behavior

The behavior of the JPA connector has a number of issues regarding entity relationships.

• Implicit joins (those needed to get child entity id's) are made INNER JOINS, preventing getting any rows where the value would be null.
• Something odd is done with *ToMany relationships which blows up the size of resultsets.
• If a parent entity and a child entity use the same name for their id property, only one gets mapped.
• It's not possible to join the same entity more than once.