Updated ModelAdmin to use form.instance when passing parent model to
child inlines for add_view. There is effectively no change in the
change_view since the previously passed 'obj' is the same as form.instance.
Thanks to meshy for report, and EvilDMP and timo for review.
``ModelAdmin.view_on_site`` defines wether to show a link to the object on the
admin detail page. If ``True``, cleverness (i.e. ``Model.get_absolute_url``) is
used to get the url. If it's a callable, the callable is called with the object
as the only parameter. If ``False``, not link is displayed.
With the aim of maitaining backwards compatibility, ``True`` is the default.
The default delete action resulted in a NoReverseMatch if it were to
list any Model with a ModelAdmin with `get_urls` overridden to remove
the change url. Catching the error and not displaying the link in that
case, as was already done for models with no registered admins.
Thanks Keryn Knight for the report.
