[FIX] ir.model: during creation of custom models, the _auto_init call should also...

[FIX] ir.model: during creation of custom models, the _auto_init call should also take care of custom fields created on-the-fly

The _auto_init call in ir.model.fields creation will not
do it because it happens before the insertion of the model
in the registry. It will only work for later addition of
fields.

bzr revid: odo@openerp.com-20130730114645-185kbupcrbtnv1tf