Fields are no longer retrieved with inspect.getmembers(), which is
time-consuming. Instead, the classes defining models automatically
collect their own fields (via Field.__set_name__()), and the field
retrieval is done by using those collections. Also, a field no longer
needs to introspect its model class to find its field definitions.
A class that defines a model automatically determines its '_name',
'_inherit' and '_module' upon creation, and the fields determine their
'name', 'model_name' and '_module' via Field.__set_name__().
Loading a registry with 290 modules from scratch is now 25% faster.
Raphael Collet
f934b29a8a