Postgres 9.4 Jsonb support

This patchset adds support for jsonb in the forthcoming Postgresql 9.4 release (currently in beta).

It correctly marshals the json data to and from the database, as well as adding support for the ? (has_key) and @> (contains) operators.

Tests are included and passing.
do these operators apply to JSON as well?  if so these should be down in JSON.comparator_factory and reused here no ?