Refactor m2m_fields to avoid a query
Refactor m2m_fields to avoid a query

This also introduces a new extension point called "_annotate_objs"
which allows you to extend the result of _get_objs.  It also receives
the original objects, which fixes #2.

Now, when you need to extend _get_objs you no longer need to loop
through the objects and group them by id (something we originally had
to do all the time)

CodeYellowBV/django-binder