[MERGE] delivery: clarified behavior when saving a delivery.carrier. We want to keep...

[MERGE] delivery: clarified behavior when saving a delivery.carrier. We want to keep the behavior of writing normal_price and free_if_more_than delivery lines. However, we also want to keep user modifications. The module now differentiates if it uses advanced pricing per destination or not. It using it, the user is responsible of the delivery grid and lines. None will be overrided. If not using it, the default behavior is used, unlinking previous lines to set normal_price and free_if_more_than.

lp bug: https://launchpad.net/bugs/927415 fixed

bzr revid: tde@openerp.com-20120214141618-w5c6ybouaqj87tqx