explicitly override db_constraint in `CustomForeignKey.__init__()`
explicitly override db_constraint in `CustomForeignKey.__init__()`

luzfcb/django-simple-history,treyhunner/django-simple-history,emergence/django-simple-history,treyhunner/django-simple-history,emergence/django-simple-history,pombredanne/django-simple-history,pombredanne/django-simple-history,luzfcb/django-simple-history