[FIX] registry: use a unique list of models to load per module

[FIX] registry: use a unique list of models to load per module

This is necessary to preserve the model loading order
as defined in the module. This was broken when the
metaclass was introduced to make the explicit model
constructor call optional.
One consequence is that the order in which the classes
are declared in the module really defines their
initialization order, even if the constructors are
later called explcitly in a different order.
This latter case should be fairly rare, and easy to
fix too - simply putting the class declaration in the
right order.

bzr revid: odo@openerp.com-20110826161736-lgnpurtbcqtbseey