Use a new hstore extension version for added json functions.

This should have been done when the json functionality was added to
hstore in 9.3.0. To handle this correctly, the upgrade script therefore
uses conditional logic by using plpgsql in a DO statement to add the two
new functions and the new cast. If hstore_to_json_loose is detected as
already present and dependent on the hstore extension nothing is done.
This will require that the database be loaded with plpgsql.

People who have installed the earlier and spurious 1.1 version of hstore
will need to do:

	ALTER EXTENSION hstore UPDATE;

to pick up the new functions properly.