possible inheritance speedup trick

[rvalyi]

OpenERP doesn't tell over RPC which objects are inherited (_inherits), this sucks and forces us to to do nasty slow tests to find out if some field is inherited or not.

In fact, I just noticed that calling reading with no field to read may return the list of inheritance keys: such as for product.product:
[{'product_tmpl_id': 5, 'id': 5}]

May be we can use that info to speed up the tests. Of course, if OpenERP could just expose that information that would just be better.