[newforms-admin] - Standard 403 error page on breadcrumb if no 'change' permission

[Alen Ribic]

If permission is restricted to only allow 'user' or 'group' to 'add' model, then breadcrumb raises a 403 error if clicked on from the add view form.

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<a>Home</a> > <a>ModelToChange</a> > Add Add  
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Middle one shouldn't be a link if there is no 'change' permission.

[Alen Ribic]

To clarify the above "Description":

If permission is restricted to only allow 'user' or 'group' to 'add' model, then breadcrumb takes the user to a 403 page if middle link is clicked (link to the change / list models page) from the 'add' model form.

Example:

class City(models.Model):
    short_title = models.CharField(max_length=50)

    class Meta:
        verbose_name_plural = "Cities"

1. Register the model class 'City' with the Admin Site.
   
2. Give a 'user' or a 'group' permission to only be able to 'add' 'City'. (So no 'change' or 'delete' permission.)
   
3. As the 'user' or user in the 'group' login and click 'add' next to 'City' from the main screen.
   
4. Now click the middle link in the breadcrumb called 'Cities'. (This is a the "change"/list page for the model.)
   

This escapes the admin interface screen and brings up the standard 403 Permission Denied page.
Middle link, "Cities", shouldn't be a link if there is no 'change' permission.

How breadcrumb should be in this scenario:

Home > <should-NOT-be-link>Cities<should-NOT-be-link> > <should-be-link>Add City</should-be-link>

[Karen Tracey <kmtracey@…>]

Trunk has the same behavior, this should not block merge.