Problems with Boolean Representation with Postgres

OPENJPA-2558 addressed, in general, boolean representations on the database (native Boolean column types, as an int(0,1), as a string, as a char, etc), but had coverage gaps with respect to the supported platforms.  Postgres is one of those platforms.  Its dictionary class still overrode setBoolean(), but did not equally override getBoolean() which introduced a conflict.

I'm proposing an update which removes the setBoolean() method from the Postgres dbdictionary, as well as adding the ability for a database platform to declare a default boolean representation type (preserving the INT10 default, but setting Postgres' to BooleanRepresentation in order to match what the schemagenerator for postgres creates).