Cleaned up the internal implementation of m2m fields by removing
related.py _get_fk_val(). The _get_fk_val() was doing the wrong thing
if asked for the foreign key value on foreign key to parent model's
primary key when child model had different primary key field.
Christopher Medrela
Jason Myers
Anssi Kääriäinen
Alasdair Nicol
Florian Apolloner