Refactoring of the JPA provider packages

[Andrus Adamchik]

Our initial JPA sub-packages breakdown doesn't make much sense now  
(jpa, jpa.cspi, jpa.spi, jpa.instrument). I am going to do some  
refactoring, moving things around a bit. I want to try a few  
scenarios and see what looks best. AFAIK, nobody has any substantial  
uncommitted JPA changes locally at the moment, anyways I wanted to  
give a heads up.

Andrus