Support indirect model delegation

[trinhanhngoc]

class Alias(models.Model):
    _name = 'mail.alias'

    alias_domain = fields.Char('Alias domain', compute='_compute_alias_domain')

class AliasMixin(models.AbstractModel):
    _name = 'mail.alias.mixin'
    _inherits = {'mail.alias': 'alias_id'}

class Project(models.Model):
    _name = "project.project"
    _inherit = ['mail.alias.mixin']

    def xxx(self):
        self.alias_domain  # should recognize alias_domain field