We make the assignation twice if any field has a context defined. This ensures
that the context will be evaluated with all initialized values when
the target records will be instantiated.
issue8586
review282041002
This is a valid depends value for a field but the __init__ method lose the
second _parent_ once it has been instantiated a first time.
Setting _parent_ value must be done recursively.
issue6441
review40261002
Cédric Krier