On large recordsets I got some severe performance issues while browsing through an inherits relation.
For example I have a batch process exporting a csv file with products variants:

I have to export 50.000 products.

If I do :
`variant.categ_id` It takes a very long time to get the result.

If I do:
`variant.product_tmpl_id.categ_id` The result is immediate

The problem is that the global perfomance of the application is impacted by this problem.

For example my POS takes more than 15 minutes to load. Because I have 26.000 products and the compute price method uses a lot browsing through the inherits such like `product.cated_id`, `product.uom_id` and they all takes a huge time to compute.

Same issue in this case.

If I do :
`variant.price` It takes a very long time to get the result.

If I do:
`variant.product_tmpl_id.price` The result is immediate

Could you help me ?


Simple way to reproduce:

1/ Create a new database and install sale module
2/ Launch following script through odoo shell :

```python
# -*- coding: utf-8 -*-
import logging

_logger = logging.getLogger(__name__)
self = self  # noqa

nb_product = 50000

i = 0
while i < nb_product:
    prod = self.env['product.template'].create({'name': 'product_%s' % i})
    i += 1
    if i % 1000 == 0:
        self.env.cr.commit()
        _logger.info("%s Products Created" % i)
```

2/ Launch following script through odoo shell :
```python
# -*- coding: utf-8 -*-
import logging

_logger = logging.getLogger(__name__)
self = self  # noqa


products = self.env['product.product'].search([])

for product in products:
    # Immediate response
    _logger.info('Category Template %s' % product.product_tmpl_id.categ_id)
    # Lagging response
    _logger.info('Category Variant %s' % product.categ_id) 
    break
```
""" stuff to do right after the registry is built """
        pass
    @classmethod
    def _patch_method(cls, name, method):
        """ Monkey-patch a method for all instances of this model. This replaces
            the method called ``name`` by ``method`` in the given class.
            The original method is then accessible via ``method.origin``, and it
            can be restored with :meth:`~._revert_method`.
            Example::
                @api.multi
                def do_write(self, values):
                    # do stuff, and call the original method
                    return do_write.origin(self, values)
                # patch method write of model
                model._patch_method('write', do_write)
                # this will call do_write
                records = model.search([...])
                records.write(...)
                # restore the original method
                model._revert_method('write')
        """
        origin = getattr(cls, name)
        method.origin = origin
        
        wrapped = api.guess(api.propagate(origin, method))
        wrapped.origin = origin
        setattr(cls, name, wrapped)
    @classmethod
    def _revert_method(cls, name):